Enzo 2.1 documentation

If you’re adding new physics to Enzo, chances are you’ll need to add some kind of new operator.

• Operator split from everything else
• Completely local, so depends on the field value and their derivatives in a cell.
• Doesn’t depend on the grid’s position in the hierarchy.

Global operators, such as solution to Poisson’s equation, are much more significant undertakings, and should be discussed with the Enzo development team.

1. Read all the supporting documents found in Enzo Primary References. This is not a simple piece of software.

It’s really in your best interest to understand the basic algorithms before trying to write code to extend it. It’s much more complex than Gadget or Zeus, and much much easier to break.

1. Open EvolveHierarchy.C

2. Read it, and understand the structure. The flowcharts can help, they can be found in Enzo Flow Chart, Source Browser.

4. Write your new routine. This can either be a grid member function (old style) or a non-member function that accesses the Enzo data using the Grid Field Arrays objects (prefered method.)

5. Locate this block of code:

```      if (Grids[grid1]->GridData->SolveHydroEquations(LevelCycleCount[level],
NumberOfSubgrids[grid1], SubgridFluxesEstimate[grid1], level) == FAIL) {
fprintf(stderr, "Error in grid->SolveHydroEquations.\n");
return FAIL;
}

JBPERF_STOP("evolve-level-13"); // SolveHydroEquations()

//      fprintf(stderr, "%"ISYM": Called Hydro\n", MyProcessorNumber);

/* Solve the cooling and species rate equations. */
```

This is in the primary grid loop on this level.

1. Insert your new grid operation right before the last comment. It should look something like this:

```      if (Grids[grid1]->GridData->SolveHydroEquations(LevelCycleCount[level],
NumberOfSubgrids[grid1], SubgridFluxesEstimate[grid1], level) == FAIL) {
fprintf(stderr, "Error in grid->SolveHydroEquations.\n");
return FAIL;
}

JBPERF_STOP("evolve-level-13"); // SolveHydroEquations()

//      fprintf(stderr, "%"ISYM": Called Hydro\n", MyProcessorNumber);

/* Solve the cooling and species rate equations. */

if( YourFlag ){
if( Grids[grid1]->GridData->YourRoutine(YourArguments) == FAIL ){
fprintf(stderr,"Error in grid->YourRoutine\n");
return FAIL;
}
```

If your code isn’t a grid member, you can omit the Grids[grid1]->GridData-> part.