# Enzo Parameter List¶

The following is a largely complete list of the parameters that Enzo understands, and a brief description of what they mean. They are grouped roughly by meaning; an alphabetical list is also available. Parameters for individual test problems are also listed here.

This parameter list has two purposes. The first is to describe and explain the parameters that can be put into the initial parameter file that begins a run. The second is to provide a comprehensive list of all parameters that the code uses, including those that go into an output file (which contains a complete list of all parameters), so that users can better understand these output files.

The parameters fall into a number of categories:

**external**- These are user parameters in the sense that they can be set in the parameter file, and provide the primary means of communication between Enzo and the user.
**internal**- These are mostly not set in the parameter file (although strictly speaking they can be) and are generally used for program to communicate with itself (via the restart of output files).
**obsolete**- No longer used.
**reserved**- To be used later.

Generally the external parameters are the only ones that are modified or set, but the internal parameters can provide useful information and can sometimes be modified so I list them here as well. Some parameters are true/false or on/off boolean flags. Eventually, these may be parsed, but in the meantime, we use the common convention of 0 meaning false or off and 1 for true or on.

This list includes parameters for the Enzo 2.0 release.

## Stopping Parameters¶

`StopTime`(external)- This parameter specifies the time (in code units) when the
calculation will halt. For cosmology simulations, this variable is
automatically set by
`CosmologyFinalRedshift`.*No default.* `StopCycle`(external)- The cycle (top grid timestep) at which the calculation stops. A
value of zero indicates that this criterion is not be used.
*Default: 100,000* `StopFirstTimeAtLevel`(external)- Causes the simulation to immediately stop when a specified level is reached. Default value 0 (off), possible values are levels 1 through maximum number of levels in a given simulation.
`NumberOfOutputsBeforeExit`(external)- After this many datadumps have been written, the code will exit. If set to 0 (default), this option will not be used. Default: 0.
`StopCPUTime`(external)- Causes the simulation to stop if the wall time exceeds
`StopCPUTime`. The simulation will output if the wall time after the next top-level timestep will exceed`StopCPUTime`, assuming that the wall time elapsed during a top-level timestep the same as the previous timestep. In units of seconds. Default: 2.592e6 (30 days) `ResubmitOn`(external)- If set to 1, the simulation will stop if the wall time will exceed
`StopCPUTime`within the next top-level timestep and run a shell script defined in`ResubmitCommand`that should resubmit the job for the user. Default: 0. `ResubmitCommand`(external)- Filename of a shell script that creates a queuing (e.g. PBS)
script from two arguments, the number of processors and parameter
file. This script is run by the root processor when stopping with
`ResubmitOn`. An example script can be found in input/resubmit.sh. Default: (null)

## Initialization Parameters¶

`ProblemType`(external)- This integer specifies the type of problem to be run. Its value causes the correct problem initializer to be called to set up the grid, and also may trigger certain boundary conditions or other problem-dependent routines to be called. The possible values are listed below. Default: none.

For other problem-specific parameters follow the links below. The problems
marked with “hydro_rk” originate from the MUSCL solver package in the enzo installation directory
`src/enzo/hydro_rk`. For the 4xx radiation hydrodynamics problem types, see
the user guides in the installation directory `doc/implicit_fld` and `doc/split_fld`.

Problem Type | Description and Parameter List |
---|---|

1 | Shock Tube (1: unigrid and AMR) |

2 | Wave Pool (2) |

3 | Shock Pool (3: unigrid 2D, AMR 2D and unigrid 3D) |

4 | Double Mach Reflection (4) |

5 | Shock in a Box (5) |

6 | Implosion |

7 | SedovBlast |

8 | KH Instability |

9 | 2D/3D Noh Problem |

10 | Rotating Cylinder (10) |

11 | Radiating Shock (11) |

12 | Free Expansion (12) |

20 | Zeldovich Pancake (20) |

21 | Pressureless Collapse (21) |

22 | Adiabatic Expansion (22) |

23 | Test Gravity (23) |

24 | Spherical Infall (24) |

25 | Test Gravity: Sphere (25) |

26 | Gravity Equilibrium Test (26) |

27 | Collapse Test (27) |

28 | TestGravityMotion |

29 | TestOrbit |

30 | Cosmology Simulation (30) |

31 | Isolated Galaxy Evolution (31) |

35 | Shearing Box Simulation (35) |

40 | Supernova Restart Simulation (40) |

50 | Photon Test (50) |

60 | Turbulence Simulation |

61 | Protostellar Collapse |

62 | Cooling Test (62) |

101 | 3D Collapse Test (hydro_rk) |

102 | 1D Spherical Collapse Test (hydro_rk) |

106 | Hydro and MHD Turbulence Simulation (hydro_rk) |

107 | Put Sink from restart |

200 | 1D MHD Test |

201 | 2D MHD Test |

202 | 3D MHD Collapse Test |

203 | MHD Turbulent Collapse Test |

207 | Galaxy disk |

208 | AGN disk |

300 | Poisson solver test |

400 | Radiation-Hydrodynamics test 1 – constant fields |

401 | Radiation-Hydrodynamics test 2 – stream test |

402 | Radiation-Hydrodynamics test 3 – pulse test |

403 | Radiation-Hydrodynamics test 4 – grey Marshak test |

404/405 | Radiation-Hydrodynamics test 5 – radiating shock test |

410/411 | Radiation-Hydrodynamics test 10/11 – Static HI ionization |

412 | Radiation-Hydrodynamics test 12 – HI ionization of a clump |

413 | Radiation-Hydrodynamics test 13 – HI ionization of a steep region |

414/415 | Radiation-Hydrodynamics test 14/15 – Cosmological HI ionization |

450-452 | Free-streaming radiation tests |

`TopGridRank`(external)- This specifies the dimensionality of the root grid and by extension the entire hierarchy. It should be 1,2 or 3. Default: none
`TopGridDimensions`(external)- This is the dimension of the top or root grid. It should consist of
1, 2 or 3 integers separated by spaces. For those familiar with the
KRONOS or ZEUS method of specifying dimensions, these values do not
include ghost or boundary zones. A dimension cannot be less than 3
zones wide and more than
`MAX_ANY_SINGLE_DIRECTION`-`NumberOfGhostZones`*2.`MAX_ANY_SINGLE_DIRECTION`is defined in`fortran.def`. Default: none `DomainLeftEdge`,`DomainRightEdge`(external)- These float values specify the two corners of the problem domain (in code units). The defaults are: 0 0 0 for the left edge and 1 1 1 for the right edge.
`LeftFaceBoundaryCondition`,`RightFaceBoundaryCondition`(external)- These two parameters each consist of vectors of integers (of length
`TopGridRank`). They specify the boundary conditions for the top grid (and hence the entire hierarchy). The first integer corresponds to the x-direction, the second to the y-direction and the third, the z-direction. The possible values are: 0 - reflecting, 1 - outflow, 2 - inflow, 3 - periodic, 4 - shearing. For inflow, the inflow values can be set through the next parameter, or more commonly are controlled by problem-specific code triggered by the`ProblemType`. For shearing boundaries, the boundary pair in another direction must be periodic. Note that self gravity will not be consistent with shearing boundary conditions. Default: 0 0 0 `ShearingVelocityDirection`(external)- Select direction of shearing boundary. Default is x direction. Changing this is probably not a good idea.
`AngularVelocity`(external)- The value of the angular velocity in the shearing boundary. Default: 0.001
`VelocityGradient`(external)- The value of the per code length gradient in the angular velocity in the shearing boundary. Default: 1.0
`BoundaryConditionName`(external)- While the above parameters provide an easy way to set an entire side of grid to a given boundary value, the possibility exists to set the boundary conditions on an individual cell basis. This is most often done with problem specific code, but it can also be set by specifying a file which contains the information in the appropriate format. This is too involved to go into here. Default: none
`InitialTime`(internal)- The time, in code units, of the current step. For cosmology the
units are in free-fall times at the initial epoch (see
*Enzo Output Formats*). Default: generally 0, depending on problem `Initialdt`(internal)- The timestep, in code units, for the current step. For cosmology
the units are in free-fall times at the initial epoch (see
*Enzo Output Formats*). Default: generally 0, depending on problem

## Simulation Identifiers and UUIDs¶

These parameters help to track, identify and group datasets. For reference,
Universally Unique Identifiers (UUIDs) are
opaque identifiers using random 128-bit numbers, with an extremely low chance
of collision. (See *Simulation Names and Identifiers* for a longer
description of these parameters.)

`MetaDataIdentifier`(external)- This is a character string without spaces (specifically, something that can be picked by “%s”), that can be defined in a parameter file, and will be written out in every following output, if it is found.
`MetaDataSimulationUUID`(internal)- A UUID that will be written out in all of the following outputs.
Like
`MetaDataIdentifier`, an existing UUID will be kept, but if one is not found, and new one will be generated. `MetaDataDatasetUUID`(internal)- A UUID created for each specific output.
`MetaDataRestartDatasetUUID`(internal)- If a
`MetaDataDatasetUUID`UUID is found when the parameter file is read in, it will written to the following datasets. This is used to track simulations across restarts and parameter adjustments. `MetaDataInitialConditionsUUID`(internal)- This is similar to
`MetaDataRestartDatasetUUID`, except it’s used to track which initial conditions were used.

## I/O Parameters¶

There are three ways to specify the frequency of outputs:
time-based, cycle-based (a cycle is a top-grid timestep), and, for
cosmology simulations, redshift-based. There is also a shortened
output format intended for visualization (movie format). Please
have a look at *Controlling Enzo data output* for more information.

`dtDataDump`(external)- The time interval, in code units, between time-based outputs. A value of 0 turns off the time-based outputs. Default: 0
`CycleSkipDataDump`(external)- The number of cycles (top grid timesteps) between cycle-based outputs. Zero turns off the cycle-based outputs. Default: 0
`DataDumpName`(external)- The base file name used for both time and cycle based outputs. Default: data
`RedshiftDumpName`(external)- The base file name used for redshift-based outputs (this can be
overridden by the
`CosmologyOutputRedshiftName`parameter). Normally a four digit identification number is appended to the end of this name, starting from 0000 and incrementing by one for every output. This can be over-ridden by including four consecutive R’s in the name (e.g. RedshiftRRRR) in which case the an identification number will not be appended but the four R’s will be converted to a redshift with an implied decimal point in the middle (i.e. z=1.24 becomes 0124). Default: RedshiftOutput `CosmologyOutputRedshift[NNNN]`(external)- The time and cycle-based outputs occur regularly at constant
intervals, but the redshift outputs are specified individually.
This is done by the use of this statement, which sets the output
redshift for a specific identification number (this integer is
between 0000 and 9999 and is used in forming the name). So the
statement
`CosmologyOutputRedshift[1] = 4.0`will cause an output to be written out at z=4 with the name RedshiftOutput0001 (unless the base name is changed either with the previous parameter or the next one). This parameter can be repeated with different values for the number (NNNN) Default: none `CosmologyOutputRedshiftName[NNNN]`(external)- This parameter overrides the parameter
`RedshiftOutputName`for this (only only this) redshift output. Can be used repeatedly in the same manner as the previous parameter. Default: none `OutputFirstTimeAtLevel`(external)- This forces Enzo to output when a given level is reached, and at every level thereafter. Default is 0 (off). User can usefully specify anything up to the maximum number of levels in a given simulation.
`FileDirectedOutput`- If this parameter is set to 1, whenever the finest level has finished
evolving Enzo will check for new signal files to output. (See
*Force Output Now*.) Default 1. `XrayLowerCutoffkeV`,`XrayUpperCutoffkeV`,`XrayTableFileName`(external)- These parameters are used in 2D projections (
`enzo -p ...`). The first two specify the X-ray band (observed at z=0) to be used, and the last gives the name of an ascii file that contains the X-ray spectral information. A gzipped version of this file good for bands within the 0.1 - 20 keV range is provided in the distribution in`input/lookup_metal0.3.data`. If these parameters are specified, then the second field is replaced with integrated emissivity along the line of sight in units of 10^{-23}erg/cm^{2}/s. Default:`XrayLowerCutoffkeV = 0.5`,`XrayUpperCutoffkeV = 2.5`. `ExtractFieldsOnly`(external)- Used for extractions (enzo -x ...) when only field data are needed instead of field + particle data. Default is 1 (TRUE).
`dtRestartDump`- Reserved for future use.
`dtHistoryDump`- Reserved for future use.
`CycleSkipRestartDump`- Reserved for future use.
`CycleSkipHistoryDump`- Reserved for future use.
`RestartDumpName`- Reserved for future use.
`HistoryDumpName`- Reserved for future use.
`ParallelRootGridIO`(external)- Normally for the mpi version, the root grid is read into the root
processor and then partitioned to separate processors using communication.
However, for
very large root grids (e.g. 512
^{3}), the root processor may not have enough memory. If this toggle switch is set on (i.e. to the value 1), then each processor reads its own section of the root grid. More I/O is required (to split up the grids and particles), but it is more balanced in terms of memory.`ParallelRootGridIO`and`ParallelParticleIO`MUST be set to 1 (TRUE) for runs involving > 64 cpus! Default: 0 (FALSE). See also`Unigrid`below. `Unigrid`(external)- This parameter should be set to 1 (TRUE) for large cases–AMR as
well as non-AMR–where the root grid is 512
^{3}or larger. This prevents initialization under subgrids at start up, which is unnecessary in cases with simple non-nested initial conditions. Unigrid must be set to 0 (FALSE) for cases with nested initial conditions. Default: 0 (FALSE). See also`ParallelRootGridIO`above. `UnigridTranspose`(external)- This parameter governs the fast FFT bookkeeping for Unigrid runs.
Does not work with isolated gravity. Default: 0 (FALSE). See also
`Unigrid`above. `OutputTemperature`(external)- Set to 1 if you want to output a temperature field in the datasets. Always 1 for cosmology simulations. Default: 0.
`OutputCoolingTime`(external)- Set to 1 if you want to output the cooling time in the datasets. Default: 0.
`OutputSmoothedDarkMatter`(external)- Set to 1 if you want to output a dark matter density field, smoothed by an SPH kernel. Set to 2 to also output smoothed dark matter velocities and velocity dispersion. Set to 0 to turn off. Default: 0.
`OutputGriddedStarParticle`(external)- Set to 1 or 2 to write out star particle data gridded onto mesh.
This will be useful e.g. if you have lots of star particles in a
galactic scale simulation. 1 will output just
`star_particle_density`; and 2 will dump`actively_forming_stellar_mass_density`,`SFR_density`, etc. Default: 0. `VelAnyl`(external)- Set to 1 if you want to output the divergence and vorticity of velocity. Works in 2D and 3D.
`BAnyl`(external)- Set to 1 if you want to output the divergence and vorticity of
`Bfield`. Works in 2D and 3D. `SmoothedDarkMatterNeighbors`(external)- Number of nearest neighbors to smooth dark matter quantities over. Default: 32.

### Streaming Data Format¶

`NewMovieLeftEdge`,`NewMovieRightEdge`(external)- These two parameters control the region for which the streaming
data are written. Default:
`DomainLeftEdge`and`DomainRightEdge`. `MovieSkipTimestep`(external)- Controls how many timesteps on a level are skipped between outputs
in the streaming data. Streaming format is off if this equals
`INT_UNDEFINED`. Default:`INT_UNDEFINED` `Movie3DVolume`(external)- Set to 1 to write streaming data as 3-D arrays. This should always be set to 1 if using the streaming format. A previous version had 2D maximum intensity projections, which now defunct. Default: 0.
`MovieVertexCentered`(external)- Set to 1 to write the streaming data interpolated to vertices. Set to 0 for cell-centered data. Default: 0.
`NewMovieDumpNumber`(internal)- Counter for streaming data files. This should equal the cycle number.
`MovieTimestepCounter`(internal)- Timestep counter for the streaming data files.
`MovieDataField`(external)- A maximum of 6 data fields can be written in the streaming format.
The data fields are specified by the array element of
BaryonField, i.e. 0 = Density, 7 = HII
Density. For writing temperature, a special value of 1000 is used.
This should be improved to be more transparent in which fields will
be written. Any element that equals
`INT_UNDEFINED`indicates no field will be written. Default:`INT_UNDEFINED`x 6 `NewMovieParticleOn`(external)- Set to 1 to write all particles in the grids. Set to 2 to write
ONLY particles that aren’t dark matter, e.g. stars. Set to 3/4 to
write ONLY particles that aren’t dark matter into a file separate
from the grid info. (For example,
`MoviePackParticle_P000.hdf5`, etc. will be the file name; this will be very helpful in speeding up the access to the star particle data, especially for the visualization or for the star particle. See`AMRH5writer.C`) Set to 0 for no particle output. Default: 0.

## Hierarchy Control Parameters¶

`StaticHierarchy`(external)- A flag which indicates if the hierarchy is static (1) or dynamic (0). In other words, a value of 1 takes the A out of AMR. Default: 1
`RefineBy`(external)- This is the refinement factor between a grid and its subgrid. For cosmology simulations, we have found a ratio of 2 to be most useful. Default: 4
`MaximumRefinementLevel`(external)- This is the lowest (most refined) depth that the code will produce. It is zero based, so the total number of levels (including the root grid) is one more than this value. Default: 2
`CellFlaggingMethod`(external)The method(s) used to specify when a cell should be refined. This is a list of integers, up to 9, as described by the following table. The methods combine in an “OR” fashion: if any of them indicate that a cell should be refined, then it is flagged. For cosmology simulations, methods 2 and 4 are probably most useful. Note that some methods have additional parameters which are described below. Default: 1

1 - refine by slope 6 - refine by Jeans length 2 - refine by baryon mass 7 - refine if (cooling time < cell width/sound speed) 3 - refine by shocks 11 - refine by resistive length 4 - refine by particle mass 12 - refine by defined region "MustRefineRegion" 5 - refine by baryon overdensity 13 - refine by metallicity (currently disabled) 101 - avoid refinement in regions defined in "AvoidRefineRegion"

`RefineRegionLeftEdge`,`RefineRegionRightEdge`(external)- These two parameters control the region in which refinement is
permitted. Each is a vector of floats (of length given by the
problem rank) and they specify the two corners of a volume.
Default: set equal to
`DomainLeftEdge`and`DomainRightEdge`. `RefineRegionAutoAdjust`(external)- This is useful for multiresolution simulations with particles in which the particles have varying mass. Set to 1 to automatically adjust the refine region at root grid timesteps to only contain high-resolution particles. This makes sure that the fine regions do not contain more massive particles which may lead to small particles orbiting them or other undesired outcomes. Setting to any integer (for example, 3) will make AdjustRefineRegion to work at (RefineRegionAutoAdjust-1)th level timesteps because sometimes the heavy particles are coming into the fine regions too fast that you need more frequent protection. Default: 0.
`RefineRegionTimeType`(external)- If set, this controls how the first column of a refinement region evolution file (see below) is interpreted, 0 for code time, 1 for redshift. Default: -1, which is equivalent to ‘off’.
`RefineRegionFile`(external)The name of a text file containing the corners of the time-evolving refinement region. The lines in the file change the values of

`RefineRegionLeft/RightEdge`during the course of the simulation, and the lines are ordered in the file from early times to late times. The first column of data is the time index (in code units or redshift, see the parameter above) for the next six columns, which are the values of`RefineRegionLeft/RightEdge`. For example, this might be two lines from the text file when time is indexed by redshift:0.60 0.530 0.612 0.185 0.591 0.667 0.208 0.55 0.520 0.607 0.181 0.584 0.653 0.201

In this case, the refinement region stays at the z=0.60 value until z=0.55, when the box moves slightly closer to the (0,0,0) corner. There is a maximum of 300 lines in the file and there is no comment header line. Default: None.

`MinimumOverDensityForRefinement`(external)These float values (up to 9) are used if the

`CellFlaggingMethod`is 2, 4 or 5. For method 2 and 4, the value is the density (baryon or particle), in code units, above which refinement occurs. When using method 5, it becomes rho [code] - 1. The elements in this array must match those in`CellFlaggingMethod`. Therefore, if`CellFlaggingMethod`= 1 4 9 10,`MinimumOverDensityForRefinement`= 0 8.0 0 0.In practice, this value is converted into a mass by multiplying it by the volume of the top grid cell. The result is then stored in the next parameter (unless that is set directly in which case this parameter is ignored), and this defines the mass resolution of the simulation. Note that the volume is of a top grid cell, so if you are doing a multi-grid initialization, you must divide this number by r

^{(d*l)}where r is the refinement factor, d is the dimensionality and l is the (zero-based) lowest level. For example, for a two grid cosmology setup where a cell should be refined whenever the mass exceeds 4 times the mean density of the subgrid, this value should be 4 / (2^{(3*1)}) = 4 / 8 = 0.5. Keep in mind that this parameter has no effect if it is changed in a restart output; if you want to change the refinement mid-run you will have to modify the next parameter. Up to 9 numbers may be specified here, each corresponding to the respective`CellFlaggingMethod`. Default: 1.5`MinimumMassForRefinement`(internal)- This float is usually set by the parameter above and so is labeled
internal, but it can be set by hand. For non-cosmological simulations, it can be the easier refinement criteria to specify. It is the mass above
which a refinement occurs if the
`CellFlaggingMethod`is appropriately set. For cosmological simulations, it is specified in units such that the entire mass in the computational volume is 1.0, otherwise it is in code units. There are 9 numbers here again, as per the above parameter. Default: none `MinimumMassForRefinementLevelExponent`(external).- This parameter modifies the behaviour of the above parameter. As it
stands, the refinement based on the
`MinimumMassForRefinement`(hereafter Mmin) parameter is complete Lagrangian. However, this can be modified. The actual mass used is Mmin*r^{(l*alpha)}where r is the refinement factor, l is the level and alpha is the value of this parameter (`MinimumMassForRefinementLevelExponent`). Therefore a negative value makes the refinement super-Lagrangian, while positive values are sub-Lagrangian. There are up to 9 values specified here, as per the above two parameters. Default: 0.0 `SlopeFlaggingFields[#]`(external)- If
`CellFlaggingMethod`is 1, and you only want to refine on the slopes of certain fields then you can enter the number IDs of the fields. Default: Refine on slopes of all fields. `MinimumSlopeForRefinement`(external)- If
`CellFlaggingMethod`is 1, then local gradients are used as the refinement criteria. All variables are examined and the relative slope is computed: abs(q(i+1)-q(i-1))/q(i). Where this value exceeds this parameter, the cell is marked for refinement. This causes problems if q(i) is near zero. This is a single integer (as opposed to the list of five for the above parameters). Entering multiple numbers here correspond to the fields listed in`SlopeFlaggingFields`. Default: 0.3 `MinimumPressureJumpForRefinement`(external)- If refinement is done by shocks, then this is the minimum (relative) pressure jump in one-dimension to qualify for a shock. The definition is rather standard (see Colella and Woodward’s PPM paper for example) Default: 0.33
`MinimumEnergyRatioForRefinement`(external)- For the dual energy formalism, and cell flagging by shock-detection, this is an extra filter which removes weak shocks (or noise in the dual energy fields) from triggering the shock detection. Default: 0.1
`MetallicityRefinementMinLevel`(external)- Sets the minimum level (maximum cell size) to which a cell enriched
with metal above a level set by
`MetallicityRefinementMinMetallicity`will be refined. This can be set to any level up to and including`MaximumRefinementLevel`. (No default setting) `MetallicityRefinementMinMetallicity`(external)- This is the threshold metallicity (in units of solar metallicity)
above which cells must be refined to a minimum level of
`MetallicityRefinementMinLevel`. Default: 1.0e-5 `MustRefineRegionMinRefinementLevel`(external)- Minimum level to which the rectangular solid volume defined by
`MustRefineRegionLeftEdge`and`MustRefineRegionRightEdge`will be refined to at all times. (No default setting) `MustRefineRegionLeftEdge`(external)- Bottom-left corner of refinement region. Must be within the overall refinement region. Default: 0.0 0.0 0.0
`MustRefineRegionRightEdge`(external)- Top-right corner of refinement region. Must be within the overall refinement region. Default: 1.0 1.0 1.0
`MustRefineParticlesRefineToLevel`(external)- The maximum level on which
`MustRefineParticles`are required to refine to. Currently sink particles and MBH particles are required to be sitting at this level at all times. Default: 0 `MustRefineParticlesRefineToLevelAutoAdjust`(external)- The parameter above might not be handy in cosmological simulations
if you want your
`MustRefineParticles`to be refined to a certain physical length, not to a level whose cell size keeps changing. This parameter (positive integer in pc) allows you to do just that. For example, if you set`MustRefineParticlesRefineToLevelAutoAdjust`= 128 (pc), then the code will automatically calculate`MustRefineParticlesRefineToLevel`using the boxsize and redshift information. Default: 0 (FALSE) `FluxCorrection`(external)- This flag indicates if the flux fix-up step should be carried out around the boundaries of the sub-grid to preserve conservation (1 - on, 0 - off). Strictly speaking this should always be used, but we have found it to lead to a less accurate solution for cosmological simulations because of the relatively sharp density gradients involved. However, it does appear to be important when radiative cooling is turned on and very dense structures are created. It does work with the ZEUS hydro method, but since velocity is face-centered, momentum flux is not corrected. Species quantities are not flux corrected directly but are modified to keep the fraction constant based on the density change. Default: 1
`InterpolationMethod`(external)There should be a whole section devoted to the interpolation method, which is used to generate new sub-grids and to fill in the boundary zones of old sub-grids, but a brief summary must suffice. The possible values of this integer flag are shown in the table below. The names specify (in at least a rough sense) the order of the leading error term for a spatial Taylor expansion, as well as a letter for possible variants within that order. The basic problem is that you would like your interpolation method to be: multi-dimensional, accurate, monotonic and conservative. There doesn’t appear to be much literature on this, so I’ve had to experiment. The first one (ThirdOrderA) is time-consuming and probably not all that accurate. The second one (SecondOrderA) is the workhorse: it’s only problem is that it is not always symmetric. The next one (SecondOrderB) is a failed experiment, and SecondOrderC is not conservative. FirstOrderA is everything except for accurate. If HydroMethod = 2 (ZEUS), this flag is ignored, and the code automatically uses SecondOrderC for velocities and FirstOrderA for cell-centered quantities. Default: 1

0 - ThirdOrderA 3 - SecondOrderC 1 - SecondOrderA 4 - FirstOrderA 2 - SecondOrderB

`ConservativeInterpolation`(external)- This flag (1 - on, 0 - off) indicates if the interpolation should be done in the conserved quantities (e.g. momentum rather than velocity). Ideally, this should be done, but it can cause problems when strong density gradients occur. This must(!) be set off for ZEUS hydro (the code does it automatically). Default: 1
`MinimumEfficiency`(external)- When new grids are created during the rebuilding process, each grid is split up by a recursive bisection process that continues until a subgrid is either of a minimum size or has an efficiency higher than this value. The efficiency is the ratio of flagged zones (those requiring refinement) to the total number of zones in the grid. This is a number between 0 and 1 and should probably by around 0.4 for standard three-dimensional runs. Default: 0.2
`NumberOfBufferZones`(external)- Each flagged cell, during the regridding process, is surrounded by a number of zones to prevent the phenomenon of interest from leaving the refined region before the next regrid. This integer parameter controls the number required, which should almost always be one. Default: 1
`RefineByJeansLengthSafetyFactor`(external)- If the Jeans length refinement criterion (see
`CellFlaggingMethod`) is being used, then this parameter specifies the number of cells which must cover one Jeans length. Default: 4 `JeansRefinementColdTemperature`(external)- If the Jeans length refinement criterion (see
`CellFlaggingMethod`) is being used, and this parameter is greater than zero, it will be used in place of the temperature in all cells. Default: -1.0 `StaticRefineRegionLevel[#]`(external)- This parameter is used to specify regions of the problem that are
to be statically refined, regardless of other parameters. This is mostly
used as an internal mechanism to keep the initial grid hierarchy in
place, but can be specified by the user. Up to 20 static regions
may be defined (this number set in
`macros_and_parameters.h`), and each static region is labeled starting from zero. For each static refined region, two pieces of information are required: (1) the region (see the next two parameters), and (2) the level at which the refinement is to occurs (0 implies a level 1 region will always exist). Default: none `StaticRefineRegionLeftEdge[#]`,`StaticRefineRegionRightEdge[#]`(external)- These two parameters specify the two corners of a statically refined region (see the previous parameter). Default: none
`AvoidRefineRegionLevel[#]`(external)- This parameter is used to limit the refinement to this level in a rectangular region. Up to MAX_STATIC_REGIONS regions can be used.
`AvoidRefineRegionLeftEdge[#]`,`AvoidRefineRegionRightEdge[#]`(external)- These two parameters specify the two corners of a region that limits refinement to a certain level (see the previous parameter). Default: none
`RefineByResistiveLength`(external)- Resistive length is defined as the curl of the magnetic field over the magnitude of the magnetic field. We make sure this length is covered by this number of cells. Default: 2
`LoadBalancing`(external)- Set to 0 to keep child grids on the same processor as their parents. Set to 1 to balance the work on one level over all processors. Set to 2 or 3 to load balance the grids but keep them on the same node. Option 2 assumes grouped scheduling, i.e. proc # = (01234567) reside on node (00112233) if there are 4 nodes. Option 3 assumes round-robin scheduling (proc = (01234567) -> node = (01230123)). Set to 4 for load balancing along a Hilbert space-filling curve on each level. Default: 1
`LoadBalancingCycleSkip`(external)- This sets how many cycles pass before we load balance the root grids. Only works with LoadBalancing set to 2 or 3. NOT RECOMMENDED for nested grid calculations. Default: 10

## Hydrodynamic Parameters¶

`UseHydro`(external)- This flag (1 - on, 0 - off) controls whether a hydro solver is used. Default: 1
`HydroMethod`(external)This integer specifies the hydrodynamics method that will be used. Currently implemented are

Hydro method Description 0 PPM DE (a direct-Eulerian version of PPM) 1 [reserved] 2 ZEUS (a Cartesian, 3D version of Stone & Norman). Note that if ZEUS is selected, it automatically turns off `ConservativeInterpolation`and the`DualEnergyFormalism`flags.3 Runge Kutta second-order based MUSCL solvers. 4 Same as 3 but including Dedner MHD (Wang & Abel 2008). For 3 and 4 there are the additional parameters `RiemannSolver`and`ReconstructionMethod`you want to set.Default: 0

More details on each of the above methods can be found at

*Hydro and MHD Methods*.`RiemannSolver`(external; only if`HydroMethod`is 3 or 4)This integer specifies the Riemann solver used by the MUSCL solver. Choice of

Riemann solver Description 0 [reserved] 1 HLL (Harten-Lax-van Leer) a two-wave, three-state solver with no resolution of contact waves 2 [reserved] 3 LLF (Local Lax-Friedrichs) 4 HLLC (Harten-Lax-van Leer with Contact) a three-wave, four-state solver with better resolution of contacts 5 TwoShock Default: 1 (HLL) for

`HydroMethod`= 3; 5 (TwoShock) for`HydroMethod`= 0`RiemannSolverFallback`(external)- If the euler update results in a negative density or energy, the solver will fallback to the HLL Riemann solver that is more diffusive only for the failing cell. Only active when using the HLLC or TwoShock Riemann solver. Default: OFF.
`ReconstructionMethod`(external; only if`HydroMethod`is 3 or 4)This integer specifies the reconstruction method for the MUSCL solver. Choice of

Reconstruction Method Description 0 PLM (piecewise linear) 1 PPM (piecwise parabolic) 2 [reserved] 3 [reserved] 4 [reserved] Default: 0 (PLM) for

`HydroMethod`= 3; 1 (PPM) for`HydroMethod`= 0`Gamma`(external)- The ratio of specific heats for an ideal gas (used by all hydro
methods). If using multiple species (i.e.
`MultiSpecies`> 0), then this value is ignored in favor of a direct calculation (except for PPM LR) Default: 5/3. `Mu`(external)- The molecular weight. Default: 0.6.
`ConservativeReconstruction`(external)- Experimental. This option turns on the reconstruction of the left/right interfaces in the Riemann problem in the conserved variables (density, momentum, and energy) instead of the primitive variables (density, velocity, and pressure). This generally gives better results in constant-mesh problems has been problematic in AMR simulations. Default: OFF
`PositiveReconstruction`(external)- Experimental and not working. This forces the Riemann solver to restrict the fluxes to always give positive pressure. Attempts to use the Waagan (2009), JCP, 228, 8609 method. Default: OFF
`CourantSafetyNumber`(external)- This is the maximum fraction of the CFL-implied timestep that will be used to advance any grid. A value greater than 1 is unstable (for all explicit methods). The recommended value is 0.4. Default: 0.6.
`RootGridCourantSafetyNumber`(external)- This is the maximum fraction of the CFL-implied timestep that will be used to advance ONLY the root grid. When using simulations with star particle creation turned on, this should be set to a value of approximately 0.01-0.02 to keep star particles from flying all over the place. Otherwise, this does not need to be set, and in any case should never be set to a value greater than 1.0. Default: 1.0.
`DualEnergyFormalism`(external)- The dual energy formalism is needed to make total energy schemes such as PPM DE and PPM LR stable and accurate in the “hyper-Machian” regime (i.e. where the ratio of thermal energy to total energy < ~0.001). Turn on for cosmology runs with PPM DE and PPM LR. Automatically turned off when used with the hydro method ZEUS. Integer flag (0 - off, 1 - on). When turned on, there are two energy fields: total energy and thermal energy. Default: 0
`DualEnergyFormalismEta1`,`DualEnergyFormalismEta2`(external)- These two parameters are part of the dual energy formalism and should probably not be changed. Defaults: 0.001 and 0.1 respectively.
`PressureFree`(external)- A flag that is interpreted by the PPM DE hydro method as an indicator that it should try and mimic a pressure-free fluid. A flag: 1 is on, 0 is off. Default: 0
`PPMFlatteningParameter`(external)- This is a PPM parameter to control noise for slowly-moving shocks. It is either on (1) or off (0). Default: 0
`PPMDiffusionParameter`(external)- This is the PPM diffusion parameter (see the Colella and Woodward method paper for more details). It is either on (1) or off (0). Default: 1 [Currently disabled (set to 0)]
`PPMSteepeningParameter`(external)- A PPM modification designed to sharpen contact discontinuities. It is either on (1) or off (0). Default: 0
`ZEUSQuadraticArtificialViscosity`(external)- This is the quadratic artificial viscosity parameter C2 of Stone & Norman, and corresponds (roughly) to the number of zones over which a shock is spread. Default: 2.0
`ZEUSLinearArtificialViscosity`(external)- This is the linear artificial viscosity parameter C1 of Stone & Norman. Default: 0.0

## Magnetohydrodynamic Parameters¶

`UseDivergenceCleaning`(external)- Method 1 and 2 are a failed experiment to do divergence cleaning using successive over relaxation. Method 3 uses conjugate gradient with a 2 cell stencil and Method 4 uses a 4 cell stencil. 4 is more accurate but can lead to aliasing effects. Default: 0
`DivergenceCleaningBoundaryBuffer`(external)- Choose to
*not*correct in the active zone of a grid by a boundary of cells this thick. Default: 0 `DivergenceCleaningThreshold`(external)- Calls divergence cleaning on a grid when magnetic field divergence is above this threshold. Default: 0.001
`PoissonApproximateThreshold`(external)- Controls the accuracy of the resulting solution for divergence cleaning Poisson solver. Default: 0.001
`ResetMagneticField`(external)- Set to 1 to reset the magnetic field in the regions that are denser than the critical matter density. Very handy when you want to re-simulate or restart the dumps with MHD. Default: 0
`ResetMagneticFieldAmplitude`(external)- The magnetic field values (in Gauss) that will be used for the above parameter. Default: 0.0 0.0 0.0

## Cosmology Parameters¶

`ComovingCoordinates`(external)- Flag (1 - on, 0 - off) that determines if comoving coordinates are used or not. In practice this turns on or off the entire cosmology machinery. Default: 0
`CosmologyFinalRedshift`(external)- This parameter specifies the redshift when the calculation will halt. Default: 0.0
`CosmologyOmegaMatterNow`(external)- This is the contribution of all non-relativistic matter (including HDM) to the energy density at the current epoch (z=0), relative to the value required to marginally close the universe. It includes dark and baryonic matter. Default: 0.279
`CosmologyOmegaLambdaNow`(external)- This is the contribution of the cosmological constant to the energy density at the current epoch, in the same units as above. Default: 0.721
`CosmologyComovingBoxSize`(external)- The size of the volume to be simulated in Mpc/h (at z=0). Default: 64.0
`CosmologyHubbleConstantNow`(external)- The Hubble constant at z=0, in units of 100 km/s/Mpc. Default: 0.701
`CosmologyInitialRedshift`(external)- The redshift for which the initial conditions are to be generated. Default: 20.0
`CosmologyMaxExpansionRate`(external)- This float controls the timestep so that cosmological terms are accurate followed. The timestep is constrained so that the relative change in the expansion factor in a step is less than this value. Default: 0.01
`CosmologyCurrentRedshift`(information only)- This is not strictly speaking a parameter since it is never interpreted and is only meant to provide information to the user. Default: n/a

## Gravity Parameters¶

`TopGridGravityBoundary`(external)- A single integer which specified the type of gravitational boundary conditions for the top grid. Possible values are 0 for periodic and 1 for isolated (for all dimensions). The isolated boundary conditions have not been tested recently, so caveat emptor. Default: 0
`SelfGravity`(external)- This flag (1 - on, 0 - off) indicates if the baryons and particles undergo self-gravity.
`GravitationalConstant`(external)- This is the gravitational constant to be used in code units. For cgs units it
should be 4*pi*G. For cosmology, this value must be 1 for the
standard units to hold. A more detailed decription can be found at
*Enzo Internal Unit System*. Default: 4*pi. `GreensFunctionMaxNumber`(external)- The Green’s functions for the gravitational potential depend on the grid size, so they are calculated on a as-needed basis. Since they are often re-used, they can be cached. This integer indicates the number that can be stored. They don’t take much memory (only the real part is stored), so a reasonable number is 100. [Ignored in current version]. Default: 1
`GreensFunctionMaxSize`- Reserved for future use.
`S2ParticleSize`(external)- This is the gravitational softening radius, in cell widths, in terms of the S2 particle described by Hockney and Eastwood in their book Computer Simulation Using Particles. A reasonable value is 3.0. [Ignored in current version]. Default: 3.0
`GravityResolution`(external)- This was a mis-guided attempt to provide the capability to increase the resolution of the gravitational mesh. In theory it still works, but has not been recently tested. Besides, it’s just not a good idea. The value (a float) indicates the ratio of the gravitational cell width to the baryon cell width. [Ignored in current version]. Default: 1
`PotentialIterations`(external)- Number of iterations to solve the potential on the subgrids. Values less than 4 sometimes will result in slight overdensities on grid boundaries. Default: 4.
`BaryonSelfGravityApproximation`(external)- This flag indicates if baryon density is derived in a strange, expensive but self-consistent way (0 - off), or by a completely reasonable and much faster approximation (1 - on). This is an experiment gone wrong; leave on. Well, actually, it’s important for very dense structures as when radiative cooling is turned on, so set to 0 if using many levels and radiative cooling is on [ignored in current version]. Default: 1
`MaximumGravityRefinementLevel`(external)- This is the lowest (most refined) depth that a gravitational
acceleration field is computed. More refined levels interpolate
from this level, provided a mechanism for instituting a minimum
gravitational smoothing length. Default:
`MaximumRefinementLevel`(unless`HydroMethod`is ZEUS and radiative cooling is on, in which case it is`MaximumRefinementLevel`- 3). `MaximumParticleRefinementLevel`(external)- This is the level at which the dark matter particle contribution to the gravity is smoothed. This works in an inefficient way (it actually smoothes the particle density onto the grid), and so is only intended for highly refined regions which are nearly completely baryon dominated. It is used to remove the discreteness effects of the few remaining dark matter particles. Not used if set to a value less than 0. Default: -1

### External Gravity Source¶

These parameters set-up an external static background gravity source that is added to the acceleration field for the baryons and particles.

`PointSourceGravity`(external)- This parameter indicates that there is to be a
(constant) gravitational field with a point source profile (
`PointSourceGravity`= 1) or NFW profile (`PointSourceGravity`= 2). Default: 0 `PointSourceGravityConstant`(external)- If
`PointSourceGravity`= 1, this is the magnitude of the point source acceleration at a distance of 1 length unit (i.e. GM in code units). If`PointSourceGravity`= 2, then it takes the mass of the dark matter halo in CGS units.`ProblemType`= 31 (galaxy disk simulation) automatically calculates values for`PointSourceGravityConstant`and`PointSourceGravityCoreRadius`. Default: 1 `PointSourceGravityCoreRadius`(external)- For
`PointSourceGravity`= 1, this is the radius inside which the acceleration field is smoothed in code units. With`PointSourceGravity`= 2, it is the scale radius, rs, in CGS units (see Navarro, Frank & White, 1997). Default: 0 `PointSourceGravityPosition`(external)- If the
`PointSourceGravity`flag is turned on, this parameter specifies the center of the point-source gravitational field in code units. Default: 0 0 0 `ExternalGravity`(external)- This fulfills the same purpose as
`PointSourceGravity`but is more aptly named.`ExternalGravity = 1`turns on an alternative implementation of the NFW profile with properties defined via the parameters`HaloCentralDensity`,`HaloConcentration`and`HaloVirialRadius`. Boxsize is assumed to be 1.0 in this case.`ExternalGravity = 10`gives a gravitational field defined by the logarithmic potential in Binney & Tremaine, corresponding to a disk with constant circular velocity. Default: 0 `ExternalGravityConstant`(external)- If
`ExternalGravity = 10`, this is the circular velocity of the disk in code units. Default: 0.0 `ExternalGravityDensity`- Reserved for future use.
`ExternalGravityPosition`(external)- If
`ExternalGravity = 10`, this parameter specifies the center of the gravitational field in code units. Default: 0 0 0 `ExternalGravityOrientation`(external)- For
`ExternalGravity = 10`, this is the unit vector of the disk’s angular momentum (e.g. a disk whose face-on view is oriented in the x-y plane would have`ExternalGravityOrientation = 0 0 1`). Default: 0 0 0 `ExternalGravityRadius`(external)- If
`ExternalGravity = 10`, this marks the inner radius of the disk in code units within which the velocity drops to zero. Default: 0.0 `UniformGravity`(external)- This flag (1 - on, 0 - off) indicates if there is to be a uniform gravitational field. Default: 0
`UniformGravityDirection`(external)- This integer is the direction of the uniform gravitational field: 0 - along the x axis, 1 - y axis, 2 - z axis. Default: 0
`UniformGravityConstant`(external)- Magnitude (and sign) of the uniform gravitational acceleration. Default: 1

## Particle Parameters¶

`ParticleBoundaryType`(external)- The boundary condition imposed on particles. At the moment, this parameter is largely ceremonial as there is only one type implemented: periodic, indicated by a 0 value. Default: 0
`ParticleCourantSafetyNumber`(external)- This somewhat strangely named parameter is the maximum fraction of a cell width that a particle is allowed to travel per timestep (i.e. it is a constant on the timestep somewhat along the lines of it’s hydrodynamic brother). Default: 0.5
`NumberOfParticles`(obsolete)- Currently ignored by all initializers, except for TestGravity and TestGravitySphere where it is the number of test points. Default: 0
`NumberOfParticleAttributes`(internal)- It is set to 3 if either
`StarParticleCreation`or`StarParticleFeedback`is set to 1 (TRUE). Default: 0 `AddParticleAttributes`(internal)- If set to 1, additional particle attributes will be added and zeroed. This is handy when restarting a run, and the user wants to use star formation afterwards. Default: 0.
`ParallelParticleIO`(external)- Normally, for the mpi version, the particle data are read into the
root processor and then distributed to separate processors.
However, for very large number of particles, the root processor may
not have enough memory. If this toggle switch is set on (i.e. to
the value 1), then Ring i/o is turned on and each processor reads
its own part of the particle data. More I/O is required, but it is
more balanced in terms of memory.
`ParallelRootGridIO`and`ParallelParticleIO`MUST be set for runs involving > 64 cpus! Default: 0 (FALSE). `ParticleSplitterIterations`(external)- Set to 1 to split particles into 13 particles (= 12 children+1
parent, Kitsionas & Whitworth (2002)). This should be ideal for
setting up an low-resolution initial condition for a relatively low
computational cost, running it for a while, and then restarting it
for an extremely high-resolution simulation in a focused region.
Currently it implicitly assumes that only DM (type=1) and
conventional star particles (type=2) inside the
`RefineRegion`get split. Other particles, which usually become Star class objects, seem to have no reason to be split. Default: 0 `ParticleSplitterChildrenParticleSeparation`(external)- This is the spacing between the child particles placed on a hexagonal close-packed (HCP) array. In the unit of a cell size which the parent particle resides in. Default: 1.0

## Parameters for Additional Physics¶

`RadiativeCooling`(external)This flag (1 - on, 0 - off) controls whether or not a radiative cooling module is called for each grid. There are currently several possibilities, controlled by the value of another flag. See

*Radiative Cooling and UV Physics Parameters*for more information on the various cooling methods. Default: 0- If the
`MultiSpecies`flag is off, then equilibrium cooling is assumed and one of the following two will happen. If the parameter`GadgetCooling`is set to 1, the primordial equilibrium code is called (see below). If`GadgetCooling`is set to 0, a file called`cool_rates.in`is read to set a cooling curve. This file consists of a set of temperature and the associated cgs cooling rate; a sample compute with a metallicity Z=0.3 Raymond-Smith code is provided in`input/cool_rates.in`. This has a cutoff at 10000 K (Sarazin & White 1987). Another choice will be`input/cool_rates.in_300K`which goes further down to 300 K (Rosen & Bregman 1995). - If the
`MultiSpecies`flag is on, then the cooling rate is computed directly by the species abundances. This routine (which uses a backward differenced multi-step algorithm) is borrowed from the Hercules code written by Peter Anninos and Yu Zhang, featuring rates from Tom Abel. Other varieties of cooling are controlled by the`MetalCooling`parameter, as discused below.

- If the
`GadgetCooling`(external)- This flag (1 - on, 0 - off) turns on (when set to 1) a set of
routines that calculate cooling rates based on the assumption of a
six-species primordial gas (H, He, no H2 or D) in equilibrium, and
is valid for temperatures greater than 10,000 K. This requires the
file
`TREECOOL`to execute. Default: 0 `MetalCooling`(external)- This flag (0 - off, 1 - metal cooling from Glover & Jappsen 2007,
2 - Cen et al (1995), 3 - Cloudy cooling from Smith, Sigurdsson, &
Abel 2008) turns on metal cooling for runs that track
metallicity. Option 1 is valid for temperatures between 100 K and
10
^{8}K because it considers fine-structure line emission from carbon, oxygen, and silicon and includes the additional metal cooling rates from Sutherland & Dopita (1993). Option 2 is only valid for temperatures above 10^{4}K. Option 3 uses multi-dimensional tables of heating/cooling values created with Cloudy and optionally coupled to the`MultiSpecies`chemistry/cooling solver. This method is valid from 10 K to 10^{8}K. See the Cloudy Cooling parameters below. Default: 0. `MetalCoolingTable`(internal)- This field contains the metal cooling table required for
`MetalCooling`option 1. In the top level directory input/, there are two files`metal_cool.dat`and`metal_cool_pop3.dat`that consider metal cooling for solar abundance and abundances from pair-instability supernovae, respectively. In the same directory, one can find an IDL routine (`make_Zcool_table.pro`) that generates these tables. Default:`metal_cool.dat` `MultiSpecies`(external)- If this flag (1, 2, 3- on, 0 - off) is on, then the code follows not just the total density, but also the ionization states of Hydrogen and Helium. If set to 2, then a nine-species model (including H2, H2+ and H-) will be computed, otherwise only six species are followed (H, H+, He, He+, He++, e-). If set to 3, then a 12 species model is followed, including D, D+ and HD. This routine, like the last one, is based on work done by Abel, Zhang and Anninos. Default: 0
`GadgetEquilibriumCooling`(external)- An implementation of the ionization equilibrium cooling code used
in the GADGET code which includes both radiative cooling and a
uniform metagalactic UV background specified by the
`TREECOOL`file (in the`amr_mpi/exe`directory). When this parameter is turned on,`MultiSpecies`and`RadiationFieldType`are forced to 0 and`RadiativeCooling`is forced to 1. [Not in public release version] `PhotoelectricHeating`(external)- If set to be 1, Gamma_pe = 5.1e-26 erg/s will be added uniformly to the gas without any shielding (Tasker & Bryan 2008). At the moment this is still experimental. Default: 0
`MultiMetals`(external)- This was added so that the user could turn on or off additional metal fields - currently there is the standard metallicity field (Metal_Density) and two additional metal fields (Z_Field1 and Z_Field2). Acceptable values are 1 or 0, Default: 0 (off).

### Cloudy Cooling¶

Cloudy cooling from Smith, Sigurdsson, & Abel (2008) interpolates
over tables of precomputed cooling data. Cloudy cooling is turned
on by setting `MetalCooling` to 3. `RadiativeCooling` must also be set
to 1. Depending on the cooling data used, it can be coupled with
`MultiSpecies` = 1, 2, or 3 so that the metal-free cooling comes from
the `MultiSpecies` machinery and the Cloudy tables provide only the
metal cooling. Datasets range in dimension from 1 to 5. Dim 1:
interpolate over temperature. Dim 2: density and temperature. Dim
3: density, metallicity, and temperature. Dim 4: density,
metallicity, electron fraction, and temperature. Dim 5: density,
metallicity, electron fraction, spectral strength, and temperature.
See Smith, Sigurdsson, & Abel (2008) for more information on
creating Cloudy datasets.

`CloudyCoolingGridFile`(external)- A string specifying the path to the Cloudy cooling dataset.
`IncludeCloudyHeating`(external)- An integer (0 or 1) specifying whether the heating rates are to be included in the calculation of the cooling. Some Cloudy datasets are made with the intention that only the cooling rates are to be used. Default: 0 (off).
`CMBTemperatureFloor`(external)- An integer (0 or 1) specifying whether a temperature floor is
created at the temperature of the cosmic microwave background
(T
_{CMB}= 2.72 (1 + z) K). This is accomplished in the code by subtracting the cooling rate at T_{CMB}such that Cooling = Cooling(T) - Cooling(T_{CMB}). Default: 1 (on). `CloudyElectronFractionFactor`(external)- A float value to account for additional electrons contributed by
metals. This is only used with Cloudy datasets with dimension
greater than or equal to 4. The value of this factor is calculated
as the sum of (A
_{i}* i) over all elements i heavier than He, where A_{i}is the solar number abundance relative to H. For the solar abundance pattern from the latest version of Cloudy, using all metals through Zn, this value is 9.153959e-3. Default: 9.153959e-3.

### Inline Halo Finding¶

Enzo can find dark matter (sub)halos on the fly with a friends-of-friends (FOF) halo finder and a subfind method, originally written by Volker Springel. All output files will be written in the directory FOF/.

`InlineHaloFinder`(external)- Set to 1 to turn on the inline halo finder. Default: 0.
`HaloFinderSubfind`(external)- Set to 1 to find subhalos inside each dark matter halo found in the friends-of-friends method. Default: 0.
`HaloFinderOutputParticleList`(external)- Set to 1 to output a list of particle positions and IDs for each (sub)halo. Written in HDF5. Default: 0.
`HaloFinderMinimumSize`(external)- Minimum number of particles to be considered a halo. Default: 50.
`HaloFinderLinkingLength`(external)- Linking length of particles when finding FOF groups. In units of cell width of the finest static grid, e.g. unigrid -> root cell width. Default: 0.1.
`HaloFinderCycleSkip`(external)- Find halos every N
^{th}top-level timestep, where N is this parameter. Not used if set to 0. Default: 3. `HaloFinderTimestep`(external)- Find halos every dt = (this parameter). Only evaluated at each top-level timestep. Not used if negative. Default: -99999.0
`HaloFinderLastTime`(internal)- Last time of a halo find. Default: 0.

### Inline Python¶

`PythonSubcycleSkip`(external)- The number of times Enzo should reach the bottom of the hierarchy before exposing its data and calling Python. Only works with python-yes in compile settings.

### Star Formation and Feedback Parameters¶

For details on each of the different star formation methods available in Enzo see *Active Particles: Stars, BH, and Sinks*.

`StarParticleCreation`(external)This parameter is bitwise so that multiple types of star formation routines can be used in a single simulation. For example if methods 1 and 3 are desired, the user would specify 10 (2

^{1}+ 2^{3}), or if methods 1, 4 and 7 are wanted, this would be 146 (2^{1}+ 2^{4}+ 2^{7}). Default: 00 - Cen & Ostriker (1992) 1 - Cen & Ostriker (1992) with stocastic star formation 2 - Global Schmidt Law / Kravstov et al. (2003) 3 - Population III stars / Abel, Wise & Bryan (2007) 4 - Sink particles: Pure sink particle or star particle with wind feedback depending on choice for HydroMethod / Wang et al. (2009) 5 - Radiative star clusters / Wise & Cen (2009) 6 - [reserved] 7 - Cen & Ostriker (1992) with no delay in formation 8 - Springel & Hernquist (2003) 9 - Massive Black Hole (MBH) particles insertion by hand / Kim et al. (2010) 10 - Population III stellar tracers

`StarParticleFeedback`(external)- This parameter works the same way as
`StarParticleCreation`but only is valid for`StarParticleCreation`= 0, 1, 2, 7 and 8 because methods 3, 5 and 9 use the radiation transport module and`Star_*.C`routines to calculate the feedback, 4 has explicit feedback and 10 does not use feedback. Default: 0. `StarFeedbackDistRadius`(external)- If this parameter is greater than zero, stellar feedback will be
deposited into the host cell and neighboring cells within this
radius. This results in feedback being distributed to a cube with
a side of
`StarFeedbackDistRadius+1`. It is in units of cell widths of the finest grid which hosts the star particle. Only implemented for`StarFeedbackCreation`= 0 or 1 with`StarParticleFeedback`= 1. (If`StarParticleFeedback`= 0, stellar feedback is only deposited into the cell in which the star particle lives). Default: 0. `StarFeedbackDistCellStep`(external)- In essence, this parameter controls the shape of the volume where
the feedback is applied, cropping the original cube. This volume
that are within
`StarFeedbackDistCellSteps`cells from the host cell, counted in steps in Cartesian directions, are injected with stellar feedback. Its maximum value is`StarFeedbackDistRadius`*`TopGridRank`. Only implemented for`StarFeedbackCreation`= 0 or 1. See*Distributed Stellar Feedback*for an illustration. Default: 0. `StarMakerTypeIaSNe`(external)- This parameter turns on thermal and chemical feedback from Type Ia
supernovae. The mass loss and luminosity of the supernovae are
determined from fits of K. Nagamine. The ejecta are
traced in a separate species field,
`MetalSNIa_Density`. The metallicity of star particles that comes from this ejecta is stored in the particle attribute`typeia_fraction`. Can be used with`StarParticleCreation`= 0, 1, 2, 5, 7, and 8. Default: 0. `StarMakerPlanetaryNebulae`(external)- This parameter turns on thermal and chemical feedback from
planetary nebulae. The mass loss and luminosity are taken from
the same fits from K. Nagamine. The chemical
feedback injects gas with the same metallicity as the star
particle, and the thermal feedback equates to a 10 km/s wind. The
ejecta are not stored in its own species field. Can be used
with
`StarParticleCreation`= 0, 1, 2, 5, 7, and 8. Default: 0.

#### Normal Star Formation¶

The parameters below are considered in `StarParticleCreation` method
0, 1, 2, 7 and 8.

`StarMakerOverDensityThreshold`(external)- The overdensity threshold in code units (for cosmological simulations, note that code units are relative to the total mean density, not
just the dark matter mean density) before star formation will be
considered. For
`StarParticleCreation`= 7 in cosmological simulations, however,`StarMakerOverDensityThreshold`should be in particles/cc, so it is not the ratio with respect to the`DensityUnits`(unlike most other star_makers). This way one correctly represents the Jeans collapse and molecular cloud scale physics even in cosmological simulations. Default: 100 `StarMakerSHDensityThreshold`(external)- The critical density of gas used in Springel & Hernquist star
formation ( \rho_{th} in the paper) used to determine the star
formation timescale in units of g cm
^{-3}. Only valid for`StarParticleCreation`= 8. Default: 7e-26. `StarMakerMassEfficiency`(external)- The fraction of identified baryonic mass in a cell (Mass*dt/t_dyn) that is converted into a star particle. Default: 1
`StarMakerMinimumMass`(external)- The minimum mass of star particle, in solar masses. Note however, the star maker algorithm 2 has a (default off) “stochastic” star formation algorithm that will, in a pseudo-random fashion, allow star formation even for very low star formation rates. It attempts to do so (relatively successfully according to tests) in a fashion that conserves the global average star formation rate. Default: 1e9
`StarMakerMinimumDynamicalTime`(external)- When the star formation rate is computed, the rate is proportional to M_baryon * dt/max(t_dyn, t_max) where t_max is this parameter. This effectively sets a limit on the rate of star formation based on the idea that stars have a non-negligible formation and life-time. The unit is years. Default: 1e6
`StarMassEjectionFraction`(external)- The mass fraction of created stars which is returned to the gas phase. Default: 0.25
`StarMetalYield`(external)- The mass fraction of metals produced by each unit mass of stars created (i.e. it is multiplied by mstar, not ejected). Default: 0.02
`StarEnergyToThermalFeedback`(external)- The fraction of the rest-mass energy of the stars created which is returned to the gas phase as thermal energy. Default: 1e-5
`StarEnergyToStellarUV`(external)- The fraction of the rest-mass energy of the stars created which is returned as UV radiation with a young star spectrum. This is used when calculating the radiation background. Default: 3e-6
`StarEnergyToQuasarUV`(external)- The fraction of the rest-mass energy of the stars created which is returned as UV radiation with a quasar spectrum. This is used when calculating the radiation background. Default: 5e-6

#### Population III Star Formation¶

The parameters below are considered in `StarParticleCreation` method 3.

`PopIIIStarMass`(external)- Stellar mass of Population III stars created in
`StarParticleCreation`method 3. Units of solar masses. The luminosities and supernova energies are calculated from Schaerer (2002) and Heger & Woosley (2002), respectively. `PopIIIBlackHoles`(external)- Set to 1 to create black hole particles that radiate in X-rays for stars that do not go supernova (< 140 solar masses and > 260 solar masses). Default: 0.
`PopIIIBHLuminosityEfficiency`(internal)- The radiative efficiency in which the black holes convert accretion to luminosity. Default: 0.1.
`PopIIIOverDensityThreshold`(internal)- The overdensity threshold (relative to the total mean density) before Pop III star formation will be considered. Default: 1e6.
`PopIIIH2CriticalFraction`(internal)- The H_2 fraction threshold before Pop III star formation will be considered. Default: 5e-4.
`PopIIIMetalCriticalFraction`(internal)- The metallicity threshold (relative to gas density, not solar) before Pop III star formation will be considered. Note: this should be changed to be relative to solar! Default: 1e-4.
`PopIIISupernovaRadius`(internal)- If the Population III star will go supernova (140<M<260 solar masses), this is the radius of the sphere to inject the supernova thermal energy at the end of the star’s life. Units are in parsecs. Default: 1.
`PopIIISupernovaUseColour`(internal)- Set to 1 to trace the metals expelled from supernovae. Default: 0.

#### Radiative Star Cluster Star Formation¶

The parameters below are considered in `StarParticleCreation` method 5.

`StarClusterUseMetalField`(internal)- Set to 1 to trace ejecta from supernovae. Default: 0.
`StarClusterMinDynamicalTime`(internal)- When determining the size of a star forming region, one method is to look for the sphere with an enclosed average density that corresponds to some minimum dynamical time. Observations hint that this value should be a few million years. Units are in years. Default: 1e7.
`StarClusterIonizingLuminosity`(internal)- The specific luminosity of the stellar clusters. In units of ionizing photons per solar mass. Default: 1e47.
`StarClusterSNEnergy`(internal)- The specific energy injected into the gas from supernovae in the stellar clusters. In units of ergs per solar mass. Default: 6.8e48 (Woosley & Weaver 1986).
`StarClusterSNRadius`(internal)- This is the radius of the sphere to inject the supernova thermal energy in stellar clusters. Units are in parsecs. Default: 10.
`StarClusterFormEfficiency`(internal)- Fraction of gas in the sphere to transfer from the grid to the star
particle. Recall that this sphere has a minimum dynamical time set
by
`StarClusterMinDynamicalTime`. Default: 0.1. `StarClusterMinimumMass`(internal)- The minimum mass of a star cluster particle before the formation is considered. Units in solar masses. Default: 1000.
`StarClusterCombineRadius`(internal)- It is possible to merge star cluster particles together within this specified radius. Units in parsecs. This is probably not necessary if ray merging is used. Originally this was developed to reduce the amount of ray tracing involved from galaxies with hundreds of these radiating particles. Default: 10.

#### Massive Black Hole Particle Formation¶

The parameters below are considered in StarParticleCreation method 9.

`MBHInsertLocationFilename`(external)The mass and location of the MBH particle that has to be inserted. For example, the content of the file should be in the following form. For details, see

`mbh_maker.src`. Default:`mbh_insert_location.in`#order: MBH mass (in Ms), MBH location[3], MBH creation time 100000.0 0.48530579 0.51455688 0.51467896 0.0

### Background Radiation Parameters¶

`RadiationFieldType`(external)- This integer parameter specifies the type of radiation field that is to be used. Except for
`RadiationFieldType`= 9, which should be used with`MultiSpecies`= 2, UV backgrounds can currently only be used with`MultiSpecies`= 1 (i.e. no molecular H support). The following values are used. Default: 01. Haardt & Madau spectrum with q_alpha=1.5 2. Haardt & Madau spectrum with q_alpha = 1.8 3. Modified Haardt & Madau spectrum to match observations (Kirkman & Tytler 2005). 4. H&M spectrum (q_alpha=1.5. supplemented with an X-ray Compton heating background from Madau & Efstathiou (see astro-ph/9902080) 9. a constant molecular H2 photo-dissociation rate 10. internally computed radiation field using the algorithm of Cen & Ostriker 11. same as previous, but with very, very simple optical shielding fudge 12. Haardt & Madau spectrum with q_alpha=1.57

`RadiationFieldLevelRecompute`(external)- This integer parameter is used only if the previous parameter is set to 10 or 11. It controls how often (i.e. the level at which) the internal radiation field is recomputed. Default: 0
`RadiationSpectrumNormalization`(external)- This parameter was initially used to normalize the photo-ionization
and photo-heating rates computed in the function
`RadiationFieldCalculateRates()`and then passed on to the`calc_photo_rates()`,`calc_rad()`and`calc_rates()`routines. Later, the normalization as a separate input parameter was dropped for all cases by using the rates computed in`RadiationFieldCalculateRates()`with one exception: The molecular hydrogen (H2) dissociation rate. There a normalization is performed on the rate by multiplying it with`RadiationSpectrumNormalization`. Default: 1e-21 `RadiationFieldRedshift`(external)- This parameter specifies the redshift at which the radiation field is calculated. Default: 0
`RadiationShield`(external)- This parameter specifies whether the user wants to employ
approximate radiative-shielding. This parameter will be
automatically turned on when RadiationFieldType is set to 11. See
`calc_photo_rates.src`. Default: 0 `RadiationRedshiftOn`(external) The redshift at which the UV- background turns on. Default: 7.0.
`RadiationRedshiftFullOn`(external) The redshift at which the UV- background is at full strength. Between z =
`RadiationRedshiftOn`and z =`RadiationRedshiftFullOn`, the background is gradually ramped up to full strength. Default: 6.0. `RadiationRedshiftDropOff`(external) The redshift at which the- strength of the UV background is begins to gradually reduce,
reaching zero by
`RadiationRedshiftOff`. Default: 0.0. `RadiationRedshiftOff`(external) The redshift at which the UV- background is fully off. Default: 0.0.
`AdjustUVBackground`(external)- Add description. Default: 1.
`SetUVAmplitude`(external)- Add description. Default: 1.0.
`SetHeIIHeatingScale`(external)- Add description. Default: 1.8.
`RadiationSpectrumSlope`(external)- Add description. Default: 1.5.

### Minimum Pressure Support Parameters¶

`UseMinimumPressureSupport`(external)- When radiative cooling is turned on, and objects are allowed to
collapse to very small sizes so that their Jeans length is no
longer resolved, then they may undergo artificial fragmentation
and angular momentum non-conservation. To alleviate this problem,
as discussed in more detail in Machacek, Bryan & Abel (2001), a
very simple fudge was introduced: if this flag is turned on, then
a minimum temperature is applied to grids with level ==
`MaximumRefinementLevel`. This minimum temperature is that required to make each cell Jeans stable multiplied by the parameter below. More precisely, the temperature of a cell is set such that the resulting Jeans length is the square-root of the parameter`MinimumPressureSupportParameter`. So, for the default value of 100 (see below), this insures that the ratio of the Jeans length/cell size is at least 10. Default: 0 `MinimumPressureSupportParameter`(external)- This is the numerical parameter discussed above. Default: 100

### Radiative Transfer (Ray Tracing) Parameters¶

`RadiativeTransfer`(external)- Set to 1 to turn on the adaptive ray tracing following Abel, Wise &
Bryan 2007. Note that Enzo must be first recompiled after setting
`make photon-yes`. Default: 0. `RadiativeTransferRadiationPressure`(external)- Set to 1 to turn on radiation pressure created from absorbed photon packages. Default: 0
`RadiativeTransferInitialHEALPixLevel`(internal)- Chooses how many rays are emitted from radiation sources. The
number of rays in Healpix are given through # =
12x4
^{level}. Default: 3. `RadiativeTransferRaysPerCell`(external)- Determines the accuracy of the scheme by giving the minimum number of rays to cross cells. The more the better (slower). Default: 5.1.
`RadiativeTransferSourceRadius`(external)- The radius at which the photons originate from the radiation source. A positive value results in a radiating sphere. Default: 0.
`RadiativeTransferPropagationRadius`(internal)- The maximum distance a photon package can travel in one timestep. Currently unused. Default: 0.
`RadiativeTransferPropagationSpeed`(internal)- The fraction of the speed of light at which the photons travel. Default: 1.
`RadiativeTransferCoupledRateSolver`(internal)- Set to 1 to calculate the new ionization fractions and gas energies after every radiative transfer timestep. This option is highly recommended to be kept on. If not, ionization fronts will propagate too slowly. Default: 1.
`RadiativeTransferOpticallyThinH2`(external)- Set to 1 to include an optically-thin H_2 dissociating
(Lyman-Werner) radiation field. Only used if
`MultiSpecies`> 1. If`MultiSpecies`> 1 and this option is off, the Lyman-Werner radiation field will be calculated with ray tracing. Default: 1. `RadiativeTransferSplitPhotonPackage`(internal)- Once photons are past this radius, they can no longer split. In
units of kpc. If this value is negative (by default), photons can
always split. Default:
`FLOAT_UNDEFINED`. `RadiativeTransferPhotonEscapeRadius`(internal)- The number of photons that pass this distance from its source are
summed into the global variable
`EscapedPhotonCount[]`. This variable also keeps track of the number of photons passing this radius multiplied by 0.5, 1, and 2. Units are in kpc. Not used if set to 0. Default: 0. `RadiativeTransferInterpolateField`(obsolete)- A failed experiment in which we evaluate the density at the midpoint of the ray segment in each cell to calculate the optical depth. To interpolate, we need to calculate the vertex interpolated density fields. Default: 0.
`RadiativeTransferSourceClustering`(internal)- Set to 1 to turn on ray merging from combined virtual sources on a binary tree. Default: 0.
`RadiativeTransferPhotonMergeRadius`(internal)- The radius at which the rays will merge from their SuperSource, which is the luminosity weighted center of two sources. This radius is in units of the separation of two sources associated with one SuperSource. If set too small, there will be angular artifacts in the radiation field. Default: 2.5
`RadiativeTransferTimestepVelocityLimit`(external)- Limits the radiative transfer timestep to a minimum value that is determined by the cell width at the finest level divided by this velocity. Units are in km/s. Default: 100.
`RadiativeTransferPeriodicBoundary`(external)- Set to 1 to turn on periodic boundary conditions for photon packages. Default: 0.
`RadiativeTransferTraceSpectrum`(external)- reserved for experimentation. Default: 0.
`RadiativeTransferTraceSpectrumTable`(external)- reserved for experimentation. Default:
`spectrum_table.dat` `RadiationXRaySecondaryIon`(external)- Set to 1 to turn on secondary ionizations and reduce heating from X-ray radiation (Shull & van Steenberg 1985). Currently only BH and MBH particles emit X-rays. Default: 0.
`RadiationXRayComptonHeating`(external)- Set to 1 to turn on Compton heating on electrons from X-ray radiation (Ciotti & Ostriker 2001). Currently only BH and MBH particles emit X-rays. Default: 0.

### Radiative Transfer (FLD) Parameters¶

`RadiativeTransferFLD`(external)- Set to 2 to turn on the fld-based radiation solvers following Reynolds,
Hayes, Paschos & Norman, 2009. Note that you also have to compile
the source using
`make photon-yes`and a`make hypre-yes`. Note that if FLD is turned on, it will force`RadiativeCooling = 0`,`GadgetEquilibriumCooling = 0`, and`RadiationFieldType = 0`to prevent conflicts. Default: 0. `ImplicitProblem`(external)- Set to 1 to turn on the implicit FLD solver, or 3 to turn on the split FLD solver. Default: 0.
`RadHydroParamfile`(external)- Names the (possibly-different) input parameter file containing
solver options for the FLD-based solvers. These are described in
the relevant User Guides, located in
`doc/implicit_fld`and`doc/split_fld`. Default: NULL. `RadiativeTransfer`(external)- Set to 0 to avoid conflicts with the ray tracing solver above. Default: 0.
`RadiativeTransferFLDCallOnLevel`(reserved)- The level in the static AMR hierarchy where the unigrid FLD solver should be called. Currently only works for 0 (the root grid). Default: 0.
`RadiativeTransferOpticallyThinH2`(external)- Set to 0 to avoid conflicts with the built-in optically-thin H_2 dissociating field from the ray-tracing solver. Default: 1.

### Radiative Transfer (FLD) Implicit Solver Parameters¶

These parameters should be placed within the file named inRadHydroParamfilein the main parameter file. All are described in detail in the User Guide indoc/implicit_fld.

`RadHydroESpectrum`(external)- Type of assumed radiation spectrum for radiation field, Default: 1.
-1 - monochromatic spectrum at frequency h nu_{HI} = 13.6 eV 0 - power law spectrum, (nu / nu_{HI} )^(-1.5) 1 - T = 1e5 blackbody spectrum

`RadHydroChemistry`(external)- Use of hydrogen chemistry in ionization model, set to 1 to turn on the hydrogen chemistry, 0 otherwise. Default: 1.
`RadHydroHFraction`(external)- Fraction of baryonic matter comprised of hydrogen. Default: 1.0.
`RadHydroModel`(external)- Determines which set of equations to use within the solver. Default: 1.
1 - chemistry-dependent model, with case-B hydrogen II recombination coefficient. 2 - chemistry-dependent model, with case-A hydrogen II recombination coefficient. 4 - chemistry-dependent model, with case-A hydrogen II recombination coefficient, but assumes an isothermal gas energy. 10 - no chemistry, instead uses a model of local thermodynamic equilibrium to couple radiation to gas energy.

`RadHydroMaxDt`(external)- maximum time step to use in the FLD solver. Default: 1e20 (no limit).
`RadHydroMinDt`(external)- minimum time step to use in the FLD solver. Default: 0.0 (no limit).
`RadHydroInitDt`(external)- initial time step to use in the FLD solver. Default: 1e20 (uses hydro time step).
`RadHydroDtNorm`(external)- type of p-norm to use in estimating time-accuracy for predicting next time step. Default: 2.0.
0 - use the max-norm. >0 - use the specified p-norm. <0 - illegal.

`RadHydroDtRadFac`(external)- Desired time accuracy tolerance for the radiation field. Default: 1e20 (unused).
`RadHydroDtGasFac`(external)- Desired time accuracy tolerance for the gas energy field. Default: 1e20 (unused).
`RadHydroDtChemFac`(external)- Desired time accuracy tolerance for the hydrogen I number density. Default: 1e20 (unused).
`RadiationScaling`(external)- Scaling factor for the radiation field, in case standard non-dimensionalization fails. Default: 1.0.
`EnergyCorrectionScaling`(external)- Scaling factor for the gas energy correction, in case standard non-dimensionalization fails. Default: 1.0.
`ChemistryScaling`(external)- Scaling factor for the hydrogen I number density, in case standard non-dimensionalization fails. Default: 1.0.
`RadiationBoundaryX0Faces`(external)- Boundary condition types to use on the x0 faces of the radiation field. Default: [0 0].
0 - Periodic. 1 - Dirichlet. 2 - Neumann.

`RadiationBoundaryX1Faces`(external)- Boundary condition types to use on the x1 faces of the radiation field. Default: [0 0].
`RadiationBoundaryX2Faces`(external)- Boundary condition types to use on the x2 faces of the radiation field. Default: [0 0].
`RadHydroLimiterType`(external)- Type of flux limiter to use in the FLD approximation. Default: 4.
0 - original Levermore-Pomraning limiter, à la Levermore & Pomraning, 1981 and Levermore, 1984. 1 - rational approximation to LP limiter. 2 - new approximation to LP limiter (to reduce floating-point cancellation error). 3 - no limiter. 4 - ZEUS limiter (limiter 2, but with no "effective albedo").

`RadHydroTheta`(external)- Time-discretization parameter to use, 0 gives explicit Euler, 1 gives implicit Euler, 0.5 gives trapezoidal. Default: 1.0.
`RadHydroAnalyticChem`(external)- Type of time approximation to use on gas energy and chemistry equations. Default: 1 (if possible for model).
0 - use a standard theta-method. 1 - use an implicit quasi-steady state (IQSS) approximation.

`RadHydroInitialGuess`(external)- Type of algorithm to use in computing the initial guess for the time-evolved solution. Default: 0.
0 - use the solution from the previous time step (safest). 1 - use explicit Euler with only spatially-local physics (heating & cooling). 2 - use explicit Euler with all physics. 5 - use an analytic predictor based on IQSS approximation of spatially-local physics.

`RadHydroNewtTolerance`(external)- Desired accuracy for solution to satisfy nonlinear residual (measured in the RMS norm). Default: 1e-6.
`RadHydroNewtIters`(external)- Allowed number of Inexact Newton iterations to achieve tolerance before returning with FAIL. Default: 20.
`RadHydroINConst`(external)- Inexact Newton constant used in specifying tolerances for inner linear solver. Default: 1e-8.
`RadHydroMaxMGIters`(external)- Allowed number of iterations for the inner linear solver (geometric multigrid). Default: 50.
`RadHydroMGRelaxType`(external)Relaxation method used by the multigrid solver. Default: 1.

:: 1 - Jacobi. 2 - Weighted Jacobi. 3 - Red/Black Gauss-Seidel (symmetric). 4 - Red/Black Gauss-Seidel (non-symmetric).

`RadHydroMGPreRelax`(external)- Number of pre-relaxation sweeps used by the multigrid solver. Default: 1.
`RadHydroMGPostRelax`(external)- Number of post-relaxation sweeps used by the multigrid solver. Default: 1.
`EnergyOpacityC0`,`EnergyOpacityC1`,`EnergyOpacityC2`,`EnergyOpacityC3`,`EnergyOpacityC4`(external)- Parameters used in defining the energy-mean opacity used with
`RadHydroModel`10. Default: [1 1 0 1 0]. `PlanckOpacityC0`,`PlanckOpacityC1`,`PlanckOpacityC2`,`PlanckOpacityC3`,`PlanckOpacityC4`(external)- Parameters used in defining the Planck-mean opacity used with
`RadHydroModel`10. Default: [1 1 0 1 0].

### Radiative Transfer (FLD) Split Solver Parameters¶

These parameters should be placed within the file named inRadHydroParamfilein the main parameter file. All are described in detail in the User Guide indoc/split_fld.

`RadHydroESpectrum`(external)- Type of assumed radiation spectrum for radiation field, Default: 1.
-1 - monochromatic spectrum at frequency h nu_{HI}= 13.6 eV 0 - power law spectrum, (nu / nu_{HI})^(-1.5) 1 - T=1e5 blackbody spectrum

`RadHydroChemistry`(external)- Use of hydrogen chemistry in ionization model, set to 1 to turn on the hydrogen chemistry, 0 otherwise. Default: 1.
`RadHydroHFraction`(external)- Fraction of baryonic matter comprised of hydrogen. Default: 1.0.
`RadHydroModel`(external)- Determines which set of equations to use within the solver. Default: 1.
- ::
- 1 - chemistry-dependent model, with case-B hydrogen II recombination
- coefficient.
- 4 - chemistry-dependent model, with case-A hydrogen II recombination
- coefficient, but assumes an isothermal gas energy.

- 10 - no chemistry, instead uses a model of local thermodynamic
- equilibrium to couple radiation to gas energy.

`RadHydroMaxDt`(external)- maximum time step to use in the FLD solver. Default: 1e20 (no limit).
`RadHydroMinDt`(external)- minimum time step to use in the FLD solver. Default: 0.0 (no limit).
`RadHydroInitDt`(external)- initial time step to use in the FLD solver. Default: 1e20 (uses hydro time step).
`RadHydroDtNorm`(external)- type of p-norm to use in estimating time-accuracy for predicting next time step. Default: 2.0.
- ::
- 0 - use the max-norm. >0 - use the specified p-norm. <0 - illegal.

`RadHydroDtRadFac`(external)- Desired time accuracy tolerance for the radiation field. Default: 1e20 (unused).
`RadHydroDtGasFac`(external)- Desired time accuracy tolerance for the gas energy field. Default: 1e20 (unused).
`RadHydroDtChemFac`(external)- Desired time accuracy tolerance for the hydrogen I number density. Default: 1e20 (unused).
`RadiationScaling`(external)- Scaling factor for the radiation field, in case standard non-dimensionalization fails. Default: 1.0.
`EnergyCorrectionScaling`(external)- Scaling factor for the gas energy correction, in case standard non-dimensionalization fails. Default: 1.0.
`ChemistryScaling`(external)- Scaling factor for the hydrogen I number density, in case standard non-dimensionalization fails. Default: 1.0.
`RadiationBoundaryX0Faces`(external)Boundary condition types to use on the x0 faces of the radiation field. Default: [0 0].

0 - Periodic. 1 - Dirichlet. 2 - Neumann.

`RadiationBoundaryX1Faces`(external)- Boundary condition types to use on the x1 faces of the radiation field. Default: [0 0].
`RadiationBoundaryX2Faces`(external)- Boundary condition types to use on the x2 faces of the radiation field. Default: [0 0].
`RadHydroTheta`(external)- Time-discretization parameter to use, 0 gives explicit Euler, 1 gives implicit Euler, 0.5 gives trapezoidal. Default: 1.0.
`RadHydroSolTolerance`(external)- Desired accuracy for solution to satisfy linear residual (measured in the 2-norm). Default: 1e-8.
`RadHydroMaxMGIters`(external)- Allowed number of iterations for the inner linear solver (geometric multigrid). Default: 50.
`RadHydroMGRelaxType`(external)Relaxation method used by the multigrid solver. Default: 1.

Jacobi. Weighted Jacobi. Red/Black Gauss-Seidel (symmetric). Red/Black Gauss-Seidel (non-symmetric).

`RadHydroMGPreRelax`(external)- Number of pre-relaxation sweeps used by the multigrid solver. Default: 1.
`RadHydroMGPostRelax`(external)- Number of post-relaxation sweeps used by the multigrid solver. Default: 1.
`EnergyOpacityC0`,`EnergyOpacityC1`,`EnergyOpacityC2`(external)- Parameters used in defining the energy-mean opacity used with RadHydroModel 10. Default: [1 1 0].

### Massive Black Hole Physics Parameters¶

Following parameters are for the accretion and feedback from the
massive black hole particle (`PARTICLE_TYPE_MBH`). More details
will soon be described in Kim et al. (2010).

#### Accretion Physics¶

`MBHAccretion`(external)- Set to 1 to turn on accretion based on the Eddington-limited
spherical Bondi-Hoyle formula (Bondi 1952). Set to 2 to turn on
accretion based on the Bondi-Hoyle formula but with fixed
temperature defined below. Set to 3 to turn on accretion with a
fixed rate defined below. Set to 4 to to turn on accretion based on
the Eddington-limited spherical Bondi-Hoyle formula, but without
v_rel in the denominator. Set to 5 to turn on accretion based on
Krumholz et al.(2006) which takes vorticity into account. Set to 6
to turn on alpha disk formalism based on DeBuhr et al.(2010).
7 and 8 are still failed experiment. Add 10 to each of these options
(i.e. 11, 12, 13, 14) to ignore the Eddington limit. See
`Star_CalculateMassAccretion.C`. Default: 0 (FALSE) `MBHAccretionRadius`(external)- This is the radius (in pc) of a gas sphere from which the accreting
mass is subtracted out at every timestep. Instead, you may want to
try set this parameter to -1, in which case an approximate Bondi
radius is calculated and used (from
`DEFAULT_MU`and`MBHAccretionFixedTemperature`). If set to -N, it will use N*(Bondi radius). See`CalculateSubtractionParameters.C`. Default: 50.0 `MBHAccretingMassRatio`(external)- There are three different scenarios you can utilize this parameter.
(1) In principle this parameter is a nondimensional factor
multiplied to the Bondi-Hoyle accretion rate; so 1.0 should give
the plain Bondi rate. (2) However, if the Bondi radius is resolved
around the MBH, the local density used to calculate Mdot can be
higher than what was supposed to be used (density at the Bondi
radius!), resulting in the overestimation of Mdot. 0.0 <
`MBHAccretingMassRatio`< 1.0 can be used to fix this. (3) Or, one might try using the density profile of R^{-1.5}to estimate the density at the Bondi radius, which is utilized when`MBHAccretingMassRatio`is set to -1. See`Star_CalculateMassAccretion.C`. Default: 1.0 `MBHAccretionFixedTemperature`(external)- This parameter (in K) is used when
`MBHAccretion = 2`. A fixed gas temperature that goes into the Bondi-Hoyle accretion rate estimation formula. Default: 3e5 `MBHAccretionFixedRate`(external)- This parameter (in Msun/yr) is used when
`MBHAccretion = 3`. Default: 1e-3 `MBHTurnOffStarFormation`(external)- Set to 1 to turn off star formation (only for
`StarParicleCreation`method 7) in the cells where MBH particles reside. Default: 0 (FALSE) `MBHCombineRadius`(external)- The distance (in pc) between two MBH particles in which two energetically-bound MBH particles merge to form one particle. Default: 50.0
`MBHMinDynamicalTime`(external)- Minimum dynamical time (in yr) for a MBH particle. Default: 1e7
`MBHMinimumMass`(external)- Minimum mass (in Msun) for a MBH particle. Default: 1e3

#### Feedback Physics¶

`MBHFeedback`(external)- Set to 1 to turn on thermal feedback of MBH particles (
`MBH_THERMAL`- not fully tested). Set to 2 to turn on mechanical feedback of MBH particles (`MBH_JETS`, bipolar jets along the total angular momentum of gas accreted onto the MBH particle so far). Set to 3 to turn on another version of mechanical feedback of MBH particles (`MBH_JETS`, always directed along z-axis). Set to 4 to turn on experimental version of mechanical feedback (MBH_JETS, bipolar jets along the total angular momentum of gas accreted onto the MBH particle so far + 10 degree random noise). Set to 5 to turn on experimental version of mechanical feedback (`MBH_JETS`, launched at random direction). Note that, even when this parameter is set to 0, MBH particles still can be radiation sources if`RadiativeTransfer`is on. See`Grid_AddFeedbackSphere.C`. Default: 0 (FALSE)``RadiativeTransfer = 0`` & ``MBHFeedback = 0`` : no feedback at all ``RadiativeTransfer = 0`` & ``MBHFeedback = 1`` : purely thermal feedback ``RadiativeTransfer = 0`` & ``MBHFeedback = 2`` : purely mechanical feedback ``RadiativeTransfer = 1`` & ``MBHFeedback = 0`` : purely radiative feedback ``RadiativeTransfer = 1`` & ``MBHFeedback = 2`` : radiative and mechanical feedback combined (one has to change the following ``MBHFeedbackRadiativeEfficiency`` parameter accordingly, say from 0.1 to 0.05, to keep the same total energy across different modes of feedback)

`MBHFeedbackRadiativeEfficiency`(external)- The radiative efficiency of a black hole. 10% is the widely accepted value for the conversion rate from the rest-mass energy of the accreting material to the feedback energy, at the innermost stable orbit of a non-spinning Schwarzschild black hole (Shakura & Sunyaev 1973, Booth & Schaye 2009). Default: 0.1
`MBHFeedbackEnergyCoupling`(external)- The fraction of feedback energy that is thermodynamically (for
`MBH_THERMAL`) or mechanically (for`MBH_JETS`) coupled to the gas. 0.05 is widely used for thermal feedback (Springel et al. 2005, Di Matteo et al. 2005), whereas 0.0001 or less is recommended for mechanical feedback depending on the resolution of the simulation (Ciotti et al. 2009). Default: 0.05 `MBHFeedbackMassEjectionFraction`(external)- The fraction of accreting mass that is returning to the gas phase.
For either
`MBH_THERMAL`or`MBH_JETS`. Default: 0.1 `MBHFeedbackMetalYield`(external)- The mass fraction of metal in the ejected mass. Default: 0.02
`MBHFeedbackThermalRadius`(external)- The radius (in pc) of a sphere in which the energy from
`MBH_THERMAL`feedback is deposited. If set to a negative value, the radius of a sphere gets bigger in a way that the sphere encloses the constant mass (= 4/3*pi*(-`MBHFeedbackThermalRadius`)^{3}Msun). The latter is at the moment very experimental; see`Star_FindFeedbackSphere.C`. Default: 50.0 `MBHFeedbackJetsThresholdMass`(external)- The bipolar jets by
`MBH_JETS`feedback are injected every time the accumulated ejecta mass surpasses`MBHFeedbackJetsThresholdMass`(in Msun). Although continuously injecting jets into the gas cells might sound great, unless the gas cells around the MBH are resolved down to Mdot, the jets make little or no dynamical impact on the surrounding gas. By imposing`MBHFeedbackJetsThresholdMass`, the jets from MBH particles are rendered intermittent, yet dynamically important. Default: 10.0 `MBHParticleIO`(external)- Set to 1 to print out basic information about MBH particles. Will
be automatically turned on if
`MBHFeedback`is set to 2 or 3. Default: 0 (FALSE) `MBHParticleIOFilename`(external)- The name of the file used for the parameter above. Default:
`mbh_particle_io.dat`

### Conduction¶

Isotropic and anisotropic thermal conduction are implemented using the method of Parrish and Stone: namely, using an explicit, forward time-centered algorithm. In the anisotropic conduction, heat can only conduct along magnetic field lines. One can turn on the two types of conduction independently, since there are situations where one might want to use both. The Spitzer fraction can be also set independently for the isotropic and anisotropic conduction.

`IsotropicConduction`(external)- Turns on isotropic thermal conduction using Spitzer conduction. Default: 0 (FALSE)
`AnisotropicConduction`(external)- Turns on anisotropic thermal conduction using Spitzer conduction.
Can only be used if MHD is turned on (
`HydroMethod`= 4). Default: 0 (FALSE) `IsotropicConductionSpitzerFraction`(external)- Prefactor that goes in front of the isotropic Spitzer conduction coefficient. Should be a value between 0 and 1. Default: 1.0
`AnisotropicConductionSpitzerFraction`(external)- Prefactor that goes in front of the anisotropic Spitzer conduction coefficient. Should be a value between 0 and 1. Default: 1.0
`ConductionCourantSafetyNumber`(external)- This is a prefactor that controls the stability of the conduction algorithm. In its current explicit formulation, it must be set to a value of 0.5 or less. Default: 0.5

### Shock Finding Parameters¶

For details on shock finding in Enzo see *Shock Finding*.

`ShockMethod`(external)This parameter controls the use and type of shock finding. Default: 0

0 - Off 1 - Temperature Dimensionally Unsplit Jumps 2 - Temperature Dimensionally Split Jumps 1 - Velocity Dimensionally Unsplit Jumps 2 - Velocity Dimensionally Split Jumps

`ShockTemperatureFloor`(external)- When calculating the mach number using temperature jumps, set the temperature floor in the calculation to this value.
`StorePreShockFields`(external)- Optionally store the Pre-shock Density and Temperature during data output.

## Test Problem Parameters¶

### Shock Tube (1: unigrid and AMR)¶

Riemann problem or arbitrary discontinuity breakup problem. The discontinuity initially separates two arbitrary constant states: Left and Right. Default values correspond to the so called Sod Shock Tube setup (test 1.1). A table below contains a series of recommended 1D tests for hydrodynamic method, specifically designed to test the performance of the Riemann solver, the treatment of shock waves, contact discontinuities, and rarefaction waves in a variety of situations (Toro 1999, p. 129).

Test LeftDensity LeftVelocity LeftPressure RightDensity RightVelocity RightPressure 1.1 1.0 0.0 1.0 0.125 0.0 0.1 1.2 1.0 -2.0 0.4 1.0 2.0 0.4 1.3 1.0 0.0 1000.0 1.0 0.0 0.01 1.4 1.0 0.0 0.01 1.0 0.0 100.0 1.5 5.99924 19.5975 460.894 5.99242 -6.19633 46.0950

`ShockTubeBoundary`(external)- Discontinuity position. Default: 0.5
`ShockTubeDirection`(external)- Discontinuity orientation. Type: integer. Default: 0 (shock(s) will propagate in x-direction)
`ShockTubeLeftDensity`,`ShockTubeRightDensity`(external)- The initial gas density to the left and to the right of the discontinuity. Default: 1.0 and 0.125, respectively
`ShockTubeLeftVelocity`,`ShockTubeRightVelocity`(external)- The same as above but for the velocity component in
`ShockTubeDirection`. Default: 0.0, 0.0 `ShockTubeLeftPressure`,`ShockTubeRightPressure`(external)- The same as above but for pressure. Default: 1.0, 0.1

### Wave Pool (2)¶

Wave Pool sets up a simulation with a 1D sinusoidal wave entering from the left boundary. The initial active region is uniform and the wave is entered via inflow boundary conditions.

`WavePoolAmplitude`(external)- The amplitude of the wave. Default: 0.01 - a linear wave.
`WavePoolAngle`(external)- Direction of wave propagation with respect to x-axis. Default: 0.0
`WavePoolDensity`(external)- Uniform gas density in the pool. Default: 1.0
`WavePoolNumberOfWaves`(external)- The test initialization will work for one wave only. Default: 1
`WavePoolPressure`(external)- Uniform gas pressure in the pool. Default: 1.0
`WavePoolSubgridLeft`,`WavePoolSubgridRight`(external)- Start and end positions of the subgrid. Default: 0.0 and 0.0 (no subgrids)
`WavePoolVelocity1(2,3)`(external)- x-,y-, and z-velocities. Default: 0.0 (for all)
`WavePoolWavelength`(external)- The wavelength. Default: 0.1 (one-tenth of the box)

### Shock Pool (3: unigrid 2D, AMR 2D and unigrid 3D)¶

The Shock Pool test sets up a system which introduces a shock from the left boundary. The initial active region is uniform, and the shock wave enters via inflow boundary conditions. 2D and 3D versions available. (D. Mihalas & B.W. Mihalas, Foundations of Radiation Hydrodynamics, 1984, p. 236, eq. 56-40.)

`ShockPoolAngle`(external)- Direction of the shock wave propagation with respect to x-axis. Default: 0.0
`ShockPoolDensity`(external)- Uniform gas density in the preshock region. Default: 1.0
`ShockPoolPressure`(external)- Uniform gas pressure in the preshock region. Default: 1.0
`ShockPoolMachNumber`(external)- The ratio of the shock velocity and the preshock sound speed. Default: 2.0
`ShockPoolSubgridLeft`,`ShockPoolSubgridRight`(external)- Start and end positions of the subgrid. Default: 0.0 and 0.0 (no subgrids)
`ShockPoolVelocity1(2,3)`(external)- Preshock gas velocity (the Mach number definition above assumes a zero velocity in the laboratory reference frame. Default: 0.0 (for all components)

### Double Mach Reflection (4)¶

A test for double Mach reflection of a strong shock (Woodward & Colella 1984). Most of the parameters are “hardwired”: d0 = 8.0, e0 = 291.25, u0 = 8.25*sqrt(3.0)/2.0, v0 = -8.25*0.5, w0 = 0.0

`DoubleMachSubgridLeft`(external)- Start position of the subgrid. Default: 0.0
`DoubleMachSubgridRight`(external)- End positions of the subgrid. Default: 0.0

### Shock in a Box (5)¶

A stationary shock front in a static 3D subgrid (Anninos et al. 1994). Initialization is done as in the Shock Tube test.

`ShockInABoxBoundary`(external)- Position of the shock. Default: 0.5
`ShockInABoxLeftDensity`,`ShockInABoxRightDensity`(external)- Densities to the right and to the left of the shock front. Default:
`dL=1.0`and`dR = dL*((Gamma+1)*m^2)/((Gamma-1)*m^2 + 2)`, where`m=2.0`and`speed=0.9*sqrt(Gamma*pL/dL)*m`. `ShockInABoxLeftVelocity`,`ShockInABoxRightVelocity`(external)- Velocities to the right and to the left of the shock front.
Default:
`vL=shockspeed`and`vR=shockspeed-m*sqrt(Gamma*pL/dL)*(1-dL/dR)`, where`m=2.0`,`shockspeed=0.9*sqrt(Gamma*pL/dL)*m`. `ShockInABoxLeftPressure`,`ShockInABoxRightPressure`(external)- Pressures to the Right and to the Left of the shock front. Default: pL=1.0 and pR=pL*(2.0*Gamma*m^2 - (Gamma-1))/(Gamma+1), where m=2.0.
`ShockInABoxSubgridLeft`,`ShockInABoxSubgridRight`(external)- Start and end positions of the subgrid. Default: 0.0 (for both)

### Rotating Cylinder (10)¶

A test for the angular momentum conservation of a collapsing cylinder of gas in an AMR simulation. Written by Brian O’Shea (oshea@msu.edu).

`RotatingCylinderOverdensity`(external)- Density of the rotating cylinder with respect to the background. Default: 20.0
`RotatingCylinderSubgridLeft`,`RotatingCylinderSubgridRight`(external)- This pair of floating point numbers creates a subgrid region at the
beginning of the simulation that will be refined to
`MaximumRefinementLevel`. It should probably encompass the whole cylinder. Positions are in units of the box, and it always creates a cube. No default value (meaning off). `RotatingCylinderLambda`(external)- Angular momentum of the cylinder as a dimensionless quantity. This is identical to the angular momentum parameter lambda that is commonly used to describe cosmological halos. A value of 0.0 is non-rotating, and 1.0 means that the gas is already approximately rotating at the Keplerian value. Default: 0.05
`RotatingCylinderTotalEnergy`(external)- Sets the default gas energy of the ambient medium, in Enzo internal units. Default: 1.0
`RotatingCylinderRadius`(external)- Radius of the rotating cylinder in units of the box size. Note that the height of the cylinder is equal to the diameter. Default: 0.3
`RotatingCylinderCenterPosition`(external)- Position of the center of the cylinder as a vector of floats. Default: (0.5, 0.5, 0.5)

### Radiating Shock (11)¶

This is a test problem similar to the Sedov test problem documented elsewhere, but with radiative cooling turned on (and the ability to useMultiSpeciesand all other forms of cooling). The main difference is that there are quite a few extras thrown in, including the ability to initialize with random density fluctuations outside of the explosion region, use a Sedov blast wave instead of just thermal energy, and some other goodies (as documented below).

`RadiatingShockInnerDensity`(external)- Density inside the energy deposition area (Enzo internal units). Default: 1.0
`RadiatingShockOuterDensity`(external)- Density outside the energy deposition area (Enzo internal units). Default: 1.0
`RadiatingShockPressure`(external)- Pressure outside the energy deposition area (Enzo internal units). Default: 1.0e-5
`RadiatingShockEnergy`(external)- Total energy deposited (in units of 1e51 ergs). Default: 1.0
`RadiatingShockSubgridLeft`,`RadiatingShockSubgridRight`(external)- Pair of floats that defines the edges of the region where the initial conditions are refined to MaximumRefinementLevel. No default value.
`RadiatingShockUseDensityFluctuation`(external)- Initialize external medium with random density fluctuations. Default: 0
`RadiatingShockRandomSeed`(external)- Seed for random number geneator (currently using Mersenne Twister). Default: 123456789
`RadiatingShockDensityFluctuationLevel`(external)- Maximum fractional fluctuation in the density level. Default: 0.1
`RadiatingShockInitializeWithKE`(external)- Initializes the simulation with some initial kinetic energy if
turned on (0 - off, 1 - on). Whether this is a simple sawtooth or a
Sedov profile is controlled by the parameter
`RadiatingShockUseSedovProfile`. Default: 0 `RadiatingShockUseSedovProfile`(external)- If set to 1, initializes simulation with a Sedov blast wave profile (thermal and kinetic energy components). If this is set to 1, it overrides all other kinetic energy-related parameters. Default: 0
`RadiatingShockSedovBlastRadius`(external)- Maximum radius of the Sedov blast, in units of the box size. Default: 0.05
`RadiatingShockKineticEnergyFraction`(external)- Fraction of the total supernova energy that is deposited as kinetic
energy. This only is used if
`RadiatingShockInitializeWithKE`is set to 1. Default: 0.0 `RadiatingShockCenterPosition`(external)- Vector of floats that defines the center of the explosion. Default: (0.5, 0.5, 0.5)
`RadiatingShockSpreadOverNumZones`(external)- Number of cells that the shock is spread over. This corresponds to a radius of approximately N * dx, where N is the number of cells and dx is the resolution of the highest level of refinement. This does not have to be an integer value. Default: 3.5

### Free Expansion (12)¶

This test sets up a blast wave in the free expansion stage. There is only kinetic energy in the sphere with the radial velocity proportional to radius. If let evolve for long enough, the problem should turn into a Sedov-Taylor blast wave.

`FreeExpansionFullBox`(external)- Set to 0 to have the blast wave start at the origin with reflecting boundaries. Set to 1 to center the problem at the domain center with periodic boundaries. Default: 0
`FreeExpansionMass`(external)- Mass of the ejecta in the blast wave in solar masses. Default: 1
`FreeExpansionRadius`(external)- Initial radius of the blast wave. Default: 0.1
`FreeExpansionDensity`(external)- Ambient density of the problem. Default: 1
`FreeExpansionEnergy`(external)- Total energy of the blast wave in ergs. Default: 1e51
`FreeExpansionMaxVelocity`(external)- Maximum initial velocity of the blast wave (at the outer radius).
If not set, a proper value is calculated using the formula in
Draine & Woods (1991). Default:
`FLOAT_UNDEFINED` `FreeExpansionTemperature`(external)- Ambient temperature of the problem in K. Default: 100
`FreeExapnsionBField`(external)- Initial uniform magnetic field. Default: 0 0 0
`FreeExpansionVelocity`(external)- Initial velocity of the ambient medium. Default: 0 0 0
`FreeExpansionSubgridLeft`(external)- Leftmost edge of the region to set the initial refinement. Default: 0
`FreeExpansionSubgridRight`(external)- Rightmost edge of the region to set the initial refinement. Default: 0

### Zeldovich Pancake (20)¶

A test for gas dynamics, expansion terms and self-gravity in both linear and non-linear regimes [Bryan thesis (1996), Sect. 3.3.4-3.3.5; Norman & Bryan (1998), Sect. 4]

`ZeldovichPancakeCentralOffset`(external)- Offset of the pancake plane. Default: 0.0 (no offset)
`ZeldovichPancakeCollapseRedshift`(external)- A free parameter which determines the epoch of caustic formation. Default: 1.0
`ZeldovichPancakeDirection`(external)- Orientation of the pancake. Type: integer. Default: 0 (along the x-axis)
`ZeldovichPancakeInitialTemperature`(external)- Initial gas temperature. Units: degrees Kelvin. Default: 100
`ZeldovichPancakeOmegaBaryonNow`(external)- Omega Baryon at redshift z=0; standard setting. Default: 1.0
`ZeldovichPancakeOmegaCDMNow`(external)- Omega CDM at redshift z=0. Default: 0 (assumes no dark matter)

### Pressureless Collapse (21)¶

An 1D AMR test for the gravity solver and advection routines: the two-sided one-dimensional collapse of a homogeneous plane parallel cloud in Cartesian coordinates. Isolated boundary conditions. Gravitational constant G=1; free fall time 0.399. The expansion terms are not used in this test. (Bryan thesis 1996, Sect. 3.3.1).

`PressurelessCollapseDirection`(external)- Coordinate direction. Default: 0 (along the x-axis).
`PressurelessCollapseInitialDensity`(external)- Initial density (the fluid starts at rest). Default: 1.0

### Adiabatic Expansion (22)¶

A test for time-integration accuracy of the expansion terms (Bryan thesis 1996, Sect. 3.3.3).

`AdiabaticExpansionInitialTemperature`(external)- Initial temperature for Adiabatic Expansion test; test example assumes 1000 K. Default: 200. Units: degrees Kelvin
`AdiabaticExpansionInitialVelocity`(external)- Initial expansion velocity. Default: 100. Units: km/s
`AdiabaticExpansionOmegaBaryonNow`(external)- Omega Baryon at redshift z=0; standard value 1.0. Default: 1.0
`AdiabaticExpansionOmegaCDMNow`(external)- Omega CDM at redshift z=0; default setting assumes no dark matter. Default: 0.0

### Test Gravity (23)¶

We set up a system in which there is one grid point with mass in order to see the resulting acceleration field. If finer grids are specified, the mass is one grid point on the subgrid as well. Periodic boundary conditions are imposed (gravity).

`TestGravityDensity`(external)- Density of the central peak. Default: 1.0
`TestGravityMotionParticleVelocity`(external)- Initial velocity of test particle(s) in x-direction. Default: 1.0
`TestGravityNumberOfParticles`(external)- The number of test particles of a unit mass. Default: 0
`TestGravitySubgridLeft`,`TestGravitySubgridRight`(external)- Start and end positions of the subgrid. Default: 0.0 and 0.0 (no subgrids)
`TestGravityUseBaryons`(external)- Boolean switch. Type: integer. Default: 0 (FALSE)

### Spherical Infall (24)¶

A test based on Bertschinger’s (1985) 3D self-similar spherical infall solution onto an initially overdense perturbation in an Einstein-de Sitter universe.

`SphericalInfallCenter`(external)- Coordinate(s) for the accretion center. Default: top grid center
`SphericalInfallFixedAcceleration`(external)- Boolean flag. Type: integer. Default: 0 (FALSE)
`SphericalInfallFixedMass`(external)- Mass used to calculate the acceleration from spherical infall
(GM/(4*pi*r^3*a)). Default: If SphericalInfallFixedMass is
undefined and
`SphericalInfallFixedAcceleration == TRUE`, then`SphericalInfallFixedMass = SphericalInfallInitialPerturbation * TopGridVolume` `SphericalInfallInitialPerturbation`(external)- The perturbation of initial mass density. Default: 0.1
`SphericalInfallOmegaBaryonNow`(external)- Omega Baryon at redshift z=0; standard setting. Default: 1.0
`SphericalInfallOmegaCDMNow`(external)- Omega CDM at redshift z=0. Default: 0.0 (assumes no dark matter) Default: 0.0
`SphericalInfallSubgridIsStatic`(external)- Boolean flag. Type: integer. Default: 0 (FALSE)
`SphericalInfallSubgridLeft`,`SphericalInfallSubgridRight`(external)- Start and end positions of the subgrid. Default: 0.0 and 0.0 (no subgrids)
`SphericalInfallUseBaryons`(external)- Boolean flag. Type: integer. Default: 1 (TRUE)

### Test Gravity: Sphere (25)¶

Sets up a 3D spherical mass distribution and follows its evolution to test the gravity solver.

`TestGravitySphereCenter`(external)- The position of the sphere center. Default: at the center of the domain
`TestGravitySphereExteriorDensity`(external)- The mass density outside the sphere. Default:
`tiny_number` `TestGravitySphereInteriorDensity`(external)- The mass density at the sphere center. Default: 1.0
`TestGravitySphereRadius`(external)- Radius of self-gravitating sphere. Default: 0.1
`TestGravitySphereRefineAtStart`(external)- Boolean flag. Type: integer. Default: 0 (FALSE)
`TestGravitySphereSubgridLeft`,`TestGravitySphereSubgridRight`(external)- Start and end positions of the subgrid. Default: 0.0 and 0.0 (no subgrids)
`TestGravitySphereType`(external)- Type of mass density distribution within the sphere. Options
include: (0) uniform density distrubution within the sphere radius;
(1) a power law with an index -2.0; (2) a power law with an index
-2.25 (the exact power law form is, e.g., r
^{-2.25}, where r is measured in units of`TestGravitySphereRadius`). Default: 0 (uniform density) `TestGravitySphereUseBaryons`(external)- Boolean flag. Type: integer . Default: 1 (TRUE)

### Gravity Equilibrium Test (26)¶

Sets up a hydrostatic exponential atmosphere with the pressure=1.0 and density=1.0 at the bottom. Assumes constant gravitational acceleration (uniform gravity field).

`GravityEquilibriumTestScaleHeight`(external)- The scale height for the exponential atmosphere . Default: 0.1

### Collapse Test (27)¶

A self-gravity test.

`CollapseTestInitialTemperature`(external)- Initial gas temperature. Default: 1000 K. Units: degrees Kelvin
`CollapseTestNumberOfSpheres`(external)- Number of spheres to collapse; must be <=
`MAX_SPHERES=10`(see`Grid.h`for definition). Default: 1 `CollapseTestRefineAtStart`(external)- Boolean flag. Type: integer. If TRUE, then initializing routine refines the grid to the desired level. Default: 1 (TRUE)
`CollapseTestUseColour`(external)- Boolean flag. Type: integer. Default: 0 (FALSE)
`CollapseTestUseParticles`(external)- Boolean flag. Type: integer. Default: 0 (FALSE)
`CollapseTestSphereCoreRadius`(external)- An array of core radii for collapsing spheres. Default: 0.1 (for all spheres)
`CollapseTestSphereDensity`(external)- An array of density values for collapsing spheres. Default: 1.0 (for all spheres)
`CollapseTestSpherePosition`(external)- A two-dimensional array of coordinates for sphere centers. Type:
float[
`MAX_SPHERES`][`MAX_DIMENSION`]. Default for all spheres: 0.5*(`DomainLeftEdge[dim]`+`DomainRightEdge[dim]`) `CollapseTestSphereRadius`(external)- An array of radii for collapsing spheres. Default: 1.0 (for all spheres)
`CollapseTestSphereTemperature`(external)- An array of temperatures for collapsing spheres. Default: 1.0. Units: degrees Kelvin
`CollapseTestSphereType`(external)- An integer array of sphere types. Default: 0
`CollapseTestSphereVelocity`(external)- A two-dimensional array of sphere velocities. Type:
float[
`MAX_SPHERES`][`MAX_DIMENSION`]. Default: 0.0 `CollapseTestUniformVelocity`(external)- Uniform velocity. Type: float[
`MAX_DIMENSION`]. Default: 0 (for all dimensions) `CollapseTestSphereMetallicity`(external)- Metallicity of the sphere in solar metallicity. Default: 0.
`CollapseTestFracKeplerianRot`(external)- Rotational velocity of the sphere in units of Keplerian velocity, i.e. 1 is rotationally supported. Default: 0.
`CollapseTestSphereTurbulence`(external)- Turbulent velocity field sampled from a Maxwellian distribution
with the temperature specified in
`CollapseTestSphereTemperature`This parameter multiplies the turbulent velocities by its value. Default: 0. `CollapseTestSphereDispersion`(external)- If using particles, this parameter multiplies the velocity dispersion of the particles by its value. Only valid in sphere type 8 (cosmological collapsing sphere from a uniform density). Default: 0.
`CollapseTestSphereCutOff`(external)- At what radius to terminate a Bonner-Ebert sphere. Units? Default: 6.5
`CollapseTestSphereAng1`(external)- Controls the initial offset (at r=0) of the rotational axis. Units in radians. Default: 0.
`CollapseTestSphereAng2`(external)- Controls the outer offset (at
`r=SphereRadius`of the rotational axis. In both`CollapseTestSphereAng1`and`CollapseTestSphereAng2`are set, the rotational axis linearly changes with radius between`CollapseTestSphereAng1`and`CollapseTestSphereAng2`. Units in radians. Default: 0. `CollapseTestSphereInitialLevel`(external)- Failed experiment to try to force refinement to a specified level. Not working. Default: 0.

### Cosmology Simulation (30)¶

A sample cosmology simulation.

`CosmologySimulationDensityName`(external)- This is the name of the file which contains initial data for baryon
density. Type: string. Example:
`GridDensity`. Default: none `CosmologySimulationTotalEnergyName`(external)- This is the name of the file which contains initial data for total energy. Default: none
`CosmologySimulationGasEnergyName`(external)- This is the name of the file which contains initial data for gas energy. Default: none
`CosmologySimulationVelocity[123]Name`(external)- These are the names of the files which contain initial data for gas
velocities.
`Velocity1`- x-component;`Velocity2`- y-component;`Velocity3`- z-component. Default: none `CosmologySimulationParticleMassName`(external)- This is the name of the file which contains initial data for particle masses. Default: none
`CosmologySimulationParticlePositionName`(external)- This is the name of the file which contains initial data for particle positions. Default: none
`CosmologySimulationParticleVelocityName`(external)- This is the name of the file which contains initial data for particle velocities. Default: none
`CosmologySimulationParticleVelocity[123]Name`(external) This is- the name of the file which contains initial data for particle
velocities but only has one component per file. This is more
useful with very large (>=2048
^{3}) datasets. Currently one can only use this in conjunction with`CosmologySimulationCalculatePositions`. because it expects a 3D grid structure instead of a 1D list of particles. Default: None. `CosmologySimulationCalculatePositions`(external)- If set to 1, Enzo will calculate the particle positions in one of two ways: 1) By using a linear Zeldo’vich approximation based on the particle velocities and a displacement factor [dln(growth factor) / dtau, where tau is the conformal time], which is stored as an attribute in the initial condition files, or 2) if the user has also defined either CosmologySimulationParticleDisplacementName or CosmologySimulationParticleDisplacement[123]Name, by reading in particle displacements from an external code and applying those directly. The latter allows the use of non-linear displacements. Default: 0.
`CosmologySimulationParticleDisplacementName`(external)- This is the name of the file which contains initial data for particle displacements. Default: none
`CosmologySimulationParticleDisplacement[123]Name`(external) This- is the name of the file which contains initial data for particle
displacements but only has one component per file. This is more
useful with very large (>=2048
^{3}) datasets. Currently one can only use this in conjunction with`CosmologySimulationCalculatePositions`. because it expects a 3D grid structure instead of a 1D list of particles. Default: None. `CosmologySimulationNumberOfInitialGrids`(external)- The number of grids at startup. 1 means top grid only. If >1, then nested grids are to be defined by the following parameters. Default: 1
`CosmologySimulationSubgridsAreStatic`(external)- Boolean flag, defines whether the subgrids introduced at the startup are static or not. Type: integer. Default: 1 (TRUE)
`CosmologySimulationGridLevel`(external)- An array of integers setting the level(s) of nested subgrids. Max
dimension
`MAX_INITIAL_GRIDS`is defined in`CosmologySimulationInitialize.C`as 10. Default for all subgrids: 1, 0 - for the top grid (grid #0) `CosmologySimulationGridDimension[#]`(external)- An array (arrays) of 3 integers setting the dimensions of nested
grids. Index starts from 1. Max number of subgrids
`MAX_INITIAL_GRIDS`is defined in`CosmologySimulationInitialize.C`as 10. Default: none `CosmologySimulationGridLeftEdge[#]`(external)- An array (arrays) of 3 floats setting the left edge(s) of nested
subgrids. Index starts from 1. Max number of subgrids
`MAX_INITIAL_GRIDS`is defined in`CosmologySimulationInitialize.C`as 10. Default: none `CosmologySimulationGridRightEdge[#]`(external)- An array (arrays) of 3 floats setting the right edge(s) of nested
subgrids. Index starts from 1. Max number of subgrids
`MAX_INITIAL_GRIDS`is defined in`CosmologySimulationInitialize.C`as 10. Default: none `CosmologySimulationUseMetallicityField`(external)- Boolean flag. Type: integer. Default: 0 (FALSE)
`CosmologySimulationInitialFractionH2I`(external)- The fraction of molecular hydrogen (H_2) at
`InitialRedshift`. This and the following chemistry parameters are used if`MultiSpecies`is defined as 1 (TRUE). Default: 2.0e-20 `CosmologySimulationInitialFractionH2II`(external)- The fraction of singly ionized molecular hydrogen (H2+) at
`InitialRedshift`. Default: 3.0e-14 `CosmologySimulationInitialFractionHeII`(external)- The fraction of singly ionized helium at
`InitialRedshift`. Default: 1.0e-14 `CosmologySimulationInitialFractionHeIII`(external)- The fraction of doubly ionized helium at
`InitialRedshift`. Default: 1.0e-17 `CosmologySimulationInitialFractionHII`(external)- The fraction of ionized hydrogen at
`InitialRedshift`. Default: 1.2e-5 `CosmologySimulationInitialFractionHM`(external)- The fraction of negatively charged hydrogen (H-) at
`InitialRedshift`. Default: 2.0e-9 `CosmologySimulationInitialFractionMetal`(external)- The fraction of metals at
`InitialRedshift`. Default: 1.0e-10 `CosmologySimulationInitialTemperature`(external)- A uniform temperature value at
`InitialRedshift`(needed if the initial gas energy field is not supplied). Default: 550*((1.0 +`InitialRedshift`)/201)^{2} `CosmologySimulationOmegaBaryonNow`(external)- This is the contribution of baryonic matter to the energy density at the current epoch (z=0), relative to the value required to marginally close the universe. Typical value 0.06. Default: 1.0
`CosmologySimulationOmegaCDMNow`(external)- This is the contribution of CDM to the energy density at the current epoch (z=0), relative to the value required to marginally close the universe. Typical value 0.94. Default: 0.0 (no dark matter)
`CosmologySimulationManuallySetParticleMassRatio`(external)- This binary flag (0 - off, 1 - on) allows the user to manually set the particle mass ratio in a cosmology simulation. Default: 0 (Enzo automatically sets its own particle mass)
`CosmologySimulationManualParticleMassRatio`(external)- This manually controls the particle mass in a cosmology simulation,
when
`CosmologySimulationManuallySetParticleMassRatio`is set to 1. In a standard Enzo simulation with equal numbers of particles and cells, the mass of a particle is set to`CosmologySimulationOmegaCDMNow`/`CosmologySimulationOmegaMatterNow`, or somewhere around 0.85 in a WMAP-type cosmology. When a different number of particles and cells are used (128 particles along an edge and 256 cells along an edge, for example) Enzo attempts to calculate the appropriate particle mass. This breaks down when`ParallelRootGridIO`and/or`ParallelParticleIO`are turned on, however, so the user must set this by hand. If you have the ratio described above (2 cells per particle along each edge of a 3D simulation) the appropriate value would be 8.0 (in other words, this should be set to (number of cells along an edge) / (number of particles along an edge) cubed. Default: 1.0.

### Isolated Galaxy Evolution (31)¶

Initializes an isolated galaxy, as per the Tasker & Bryan series of papers.

`GalaxySimulationRefineAtStart`(external)- Controls whether or not the simulation is refined beyond the root grid at initialization. (0 - off, 1 - on). Default: 1
`GalaxySimulationInitialRefinementLevel`(external)- Level to which the simulation is refined at initialization,
assuming
`GalaxySimulationRefineAtStart`is set to 1. Default: 0 `GalaxySimulationSubgridLeft`,`GalaxySimulationSubgridRight`(external)- Vectors of floats defining the edges of the volume which is refined at start. No default value.
`GalaxySimulationUseMetallicityField`(external)- Turns on (1) or off (0) the metallicity field. Default: 0
`GalaxySimulationInitialTemperature`(external)- Initial temperature that the gas in the simulation is set to. Default: 1000.0
`GalaxySimulationUniformVelocity`(external)- Vector that gives the galaxy a uniform velocity in the ambient medium. Default: (0.0, 0.0, 0.0)
`GalaxySimulationDiskRadius`(external)- Radius (in Mpc) of the galax disk. Default: 0.2
`GalaxySimulationGalaxyMass`(external)- Dark matter mass of the galaxy, in Msun. Needed to initialize the NFW gravitational potential. Default: 1.0e+12
`GalaxySimulationGasMass`(external)- Amount of gas in the galaxy, in Msun. Used to initialize the density field in the galactic disk. Default: 4.0e+10
`GalaxySimulationDiskPosition`(external)- Vector of floats defining the center of the galaxy, in units of the box size. Default: (0.5, 0.5, 0.5)
`GalaxySimulationDiskScaleHeightz`(external)- Disk scale height, in Mpc. Default: 325e-6
`GalaxySimulationDiskScaleHeightR`(external)- Disk scale radius, in Mpc. Default: 3500e-6
`GalaxySimulationDarkMatterConcentrationParameter`(external)- NFW dark matter concentration parameter. Default: 12.0
`GalaxySimulationDiskTemperature`(external)- Temperature of the gas in the galactic disk. Default: 1.0e+4
`GalaxySimulationInflowTime`(external)- Controls inflow of gas into the box. It is strongly suggested that you leave this off. Default: -1 (off)
`GalaxySimulationInflowDensity`(external)- Controls inflow of gas into the box. It is strongly suggested that you leave this off. Default: 0.0
`GalaxySimulationAngularMomentum`(external)- Unit vector that defines the angular momentum vector of the galaxy (in other words, this and the center position define the plane of the galaxy). This _MUST_ be set! Default: (0.0, 0.0, 0.0)

### Shearing Box Simulation (35)¶

`ShearingBoxProblemType`(external)- Value of 0 starts a sphere advection through the shearing box test. Value of 1 starts a standard Balbus & Hawley shearing box simulation. Default: 0
`ShearingBoxRefineAtStart`(external)- Refine the simulation at start. Default: 1.0
`ThermalMagneticRatio`(external)- Plasma beta (Pressure/Magnetic Field Energy) Default: 400.0
`FluctuationAmplitudeFraction`(external)- The magnitude of the sinusoidal velocity perturbations as a fraction of the angular velocity. Default: 0.1
`ShearingBoxGeometry`(external)- Defines the radius of the sphere for
`ShearingBoxProblemType`= 0, and the frequency of the velocity fluctuations (in units of 2pi) for`ShearingBoxProblemType`= 1. Default: 2.0

### Supernova Restart Simulation (40)¶

All of the supernova parameters are to be put into a restart dump parameter file. Note that ProblemType must be reset to 40, otherwise these are ignored.

`SupernovaRestartEjectaCenter[#]`(external)- Input is a trio of coordinates in code units where the supernova’s
energy and mass ejecta will be centered. Default:
`FLOAT_UNDEFINED` `SupernovaRestartEjectaEnergy`(external)- The amount of energy instantaneously output in the simulated supernova, in units of 1e51 ergs. Default: 1.0
`SupernovaRestartEjectaMass`(external)- The mass of ejecta in the supernova, in units of solar masses. Default: 1.0
`SupernovaRestartEjectaRadius`(external)- The radius over which the above two parameters are spread. This is important because if it’s too small the timesteps basically go to zero and the simulation takes forever, but if it’s too big then you loose information. Units are parsecs. Default: 1.0 pc
`SupernovaRestartName`(external)- This is the name of the restart data dump that the supernova problem is initializing from.
`SupernovaRestartColourField`- Reserved for future use.

### Photon Test (50)¶

This test problem is modeled after Collapse Test (27), and thus borrows all of its parameters that control the setup of spheres. Replace CollapseTest with PhotonTest in the sphere parameters, and it will be recognized. However there are parameters that control radiation sources, which makes this problem unique from collapse test. The radiation sources are fixed in space.

`PhotonTestNumberOfSources`(external)- Sets the number of radiation sources. Default: 1.
`PhotonTestSourceType`(external)- Sets the source type. No different types at the moment. Default: 0.
`PhotonTestSourcePosition`(external)- Sets the source position. Default: 0.5*(
`DomainLeftEdge`+`DomainRightEdge`) `PhotonTestSourceLuminosity`(external)- Sets the source luminosity in units of photons per seconds. Default: 0.
`PhotonTestSourceLifeTime`(external)- Sets the lifetime of the source in units of code time. Default: 0.
`PhotonTestSourceRampTime`(external)- If non-zero, the source will exponentially increase its luminosity until it reaches the full luminosity when the age of the source equals this parameter. Default: 0.
`PhotonTestSourceEnergyBins`(external)- Sets the number of energy bins in which the photons are emitted from the source. Default: 4.
`PhotonTestSourceSED`(external)- An array with the fractional luminosity in each energy bin. The sum of this array must equal to one. Default: 1 0 0 0
`PhotonTestSourceEnergy`(external)- An array with the mean energy in each energy bin. Units are in eV. Default: 14.6 25.6 56.4 12.0 (i.e. HI ionizing, HeI ionizing, HeII ionizing, Lyman-Werner)
`PhotonTestInitialFractionHII`(external)- Sets the initial ionized fraction of hydrogen. Default: 1.2e-5
`PhotonTestInitialFractionHeII`(external)- Sets the initial singly-ionized fraction of helium. Default: 1e-14
`PhotonTestInitialFractionHeIII`(external)- Sets the initial doubly-ionized fraction of helium. Default: 1e-17
`PhotonTestInitialFractionHM`(external)- Sets the initial fraction of H
^{-}. Default: 2e-9 `PhotonTestInitialFractionH2I`(external)- Sets the initial neutral fraction of H2. Default: 2e-20
`PhotonTestInitialFractionH2II`(external)- Sets the initial ionized fraction of H2. Default: 3e-14
`PhotonTestOmegaBaryonNow`(obsolete)- Default: 0.05.

### Cooling Test (62)¶

This test problem sets up a 3D grid varying smoothly in log-space in H number density (x dimension), metallicity (y-dimension), and temperature (z-dimension). The hydro solver is turned off. By varying theRadiativeCoolingandCoolingTestResetEnergiesparameters, two different cooling tests can be run. 1) Keep temperature constant, but iterate chemistry to allow species to converge. This will allow you to make plots of Cooling rate vs. T. For this, setRadiativeCoolingto 0 andCoolingTestResetEnergiesto 1. 2) Allow gas to cool, allowing one to plot Temperature vs. time. For this, setRadiativeCoolingto 1 andCoolingTestResetEnergiesto 0.

`CoolingTestMinimumHNumberDensity`(external)- The minimum density in code units at x=0. Default: 1
[cm
^{-3}]. `CoolingTestMaximumHNumberDensity`(external)- The maximum density in code units at
x=``DomainRightEdge[0]``. Default: 1e6
[cm
^{-3}]. `CoolingTestMinimumMetallicity`(external)- The minimum metallicity at y=0. Default: 1e-6 [Z
_{sun}]. `CoolingTestMaximumMetallicity`(external)- The maximum metallicity at
y=``DomainRightEdge[1]``. Default: 1
[Z
_{sun}]. `CoolingTestMinimumTemperature`(external)- The minimum temperature in Kelvin at z=0. Default: 10.0 [K].
`CoolingTestMaximumTemperature`(external)- The maximum temperature in Kelvin at z=``DomainRightEdge[2]``. Default: 1e7 [K].
`CoolingTestResetEnergies`(external)- An integer flag (0 or 1) to determine whether the grid energies should be continually reset after every iteration of the chemistry solver such that the temperature remains constant as the mean molecular weight varies slightly. Default: 1.

## Other External Parameters¶

`huge_number`(external)- The largest reasonable number. Rarely used. Default: 1e+20
`tiny_number`(external)A number which is smaller than all physically reasonable numbers. Used to prevent divergences and divide-by-zero in C++ functions. Modify with caution! Default: 1e-20.

An independent analog,

`tiny`, defined in`fortran.def`, does the same job for a large family of FORTRAN routines. Modification of`tiny`must be done with caution and currently requires recompiling the code, since`tiny`is not a runtime parameter.`TimeActionParameter[#]`- Reserved for future use.
`TimeActionRedshift[#]`- Reserved for future use.
`TimeActionTime[#]`- Reserved for future use.
`TimeActionType[#]`- Reserved for future use.

## Other Internal Parameters¶

`TimeLastRestartDump`- Reserved for future use.
`TimeLastDataDump`(internal)- The code time at which the last time-based output occurred.
`TimeLastHistoryDump`- Reserved for future use.
`TimeLastMovieDump`(internal)- The code time at which the last movie dump occurred.
`CycleLastRestartDump`- Reserved for future use.
`CycleLastDataDump`(internal)- The last cycle on which a cycle dump was made
`CycleLastHistoryDump`- Reserved for future use.
`InitialCPUTime`- Reserved for future use.
`InitialCycleNumber`(internal)- The current cycle
`RestartDumpNumber`- Reserved for future use.
`DataLabel[#]`(internal)- These are printed out into the restart dump parameter file. One Label is produced per baryon field with the name of that baryon field. The same labels are used to name data sets in HDF files.
`DataUnits[#]`- Reserved for future use.
`DataDumpNumber`(internal)- The identification number of the next output file (the 0000 part of the output name). This is used and incremented by both the cycle based and time based outputs. Default: 0
`HistoryDumpNumber`- Reserved for future use.
`MovieDumpNumber`(internal)- The identification number of the next movie output file. Default: 0
`VersionNumber`(internal)- Sets the version number of the code which is written out to restart dumps.