# Running Enzo with Grackle¶

The Grackle is an external chemistry and cooling library originally derived from Enzo’s MultiSpecies chemistry and Cloudy cooling modules. The non-equilibrium primordial chemistry and cooling functionality is essentially identical to the MultiSpecies network. However, significant updates have been made to the treatment of metals and UV backgrounds that may make using the Grackle a more attactive option, such as:

• UV backgrounds are treated via interpolating from data tables loaded from disk rather than piece-wise polynomial functions, making it somewhat easier to add support for new background models.

• UV background and cooling data are contained within the same input file and are more consistent than the currently available Cloudy cooling data and Enzo UV background models. Currently, the Grackle distribution comes with UV background and cooling data for two different models:

• Unlike the original Cloudy cooling which required separate input files for cooling before the UV background turns on and after, all data is contained in a single table. This means one no longer has to run with one input file to the redshift where the UV background starts, stop the simulation, and restart with another input file.

• Also unlike the original Cloudy cooling module, Grackle supports the option to also solve the primordial cooling via interpolation from a table. Thus, one is no longer required to run with the MultiSpecies functionality in order to calculate the primordial component. This simplified method is somewhat faster and requires fewer baryon fields to be stored, lowering the ram and disk footprint.

## Obtaining and Building the Grackle¶

See the Grackle documentation for complete instruction on how to obtain, compile, and install the Grackle library.

## Compiling Enzo with Grackle¶

In order to compile Enzo with support for Grackle, the following lines need to be added to your machine make file in the appropriate places:

LOCAL_GRACKLE_INSTALL = PATH/TO/GRACKLE
LOCAL_INCLUDES_GRACKLE = -I$(LOCAL_GRACKLE_INSTALL)/include MACH_INCLUDES_GRACKLE =$(LOCAL_INCLUDES_GRACKLE)
LOCAL_LIBS_GRACKLE = -L$(LOCAL_GRACKLE_INSTALL)/lib -lgrackle MACH_LIBS_GRACKLE =$(LOCAL_LIBS_GRACKLE)


See the example make file, Make.mach.unkown, in the Enzo source for an example.

To configuration Enzo to build with Grackle support, do the following before typing “make”:

make grackle-yes


## Running with the Grackle¶

Grackle parameters should be given in the same parameter file as the rest of the Enzo parameters. Since the Grackle is based on Enzo’s MultiSpecies, many of the parameter names are the same. For a full list of Grackle parameters, see here.