# Advanced

## Testing / debugging

The following inputs must be preceded by “mfix.”

| Description | Type | Default
--- | --- | --- | ---
verbose | Verbosity in MFIX-Exa routines | Int | 0
ooo_debug | If true then print the name of the routine we are in | Bool | False
only_print_grid_report | Do not time-march the simulation. Simply generate the grid report and exit. | Bool | False

The following inputs must be preceded by “amrex.”

| Description | Type | Default
--- | --- | --- | ---
fpe_trap_invalid | Abort if an invalid floating point exception is encountered. | Int | 0
fpe_trap_zero | Abort if a division by zero is computed. | Int | 0
fpe_trap_overflow | Abort if an overflow is detected. | Int | 0

## GPU memory

The following inputs must be preceded by the prefix `amrex`:

| Description | Type | Default
--- | --- | --- | ---
the_arena_is_managed | Use managed memory for the main arena. | Int | 0
the_arena_init_size | Initial size of main memory arena (bytes). If not specified, use 3/4 of system device memory. | Int | Unspecified
abort_on_out_of_gpu_memory | Abort if free device memory is less than the amount an arena is asked to allocate. | Int | 0

## Load balancing

Note that when running a granular simulation, i.e., no fluid phase, `mfix.load_balance` defaults to `SingleGrid`. Hence, the `particles.max_grid_size` (in each direction) have no meaning. Therefore the fluid grid and tile sizes should be set for particle load balancing. It may also be necessary to set the blocking factors to 1.

The following inputs must be preceded by the prefix `mfix` and control load balancing:

| Description | Type | Default
--- | --- | --- | ---
regrid_int | How often to regrid (in number of steps at level 0) if regrid_int <= 0 then no regridding will occur | int | 0
load_balance | `SingleGrid` fluid and particles are co-located on the same grids `DualGrid` fluid and particles live on different grids | string | SingleGrid
load_balance.DualGrid.fluid | Regrid mesh (fluid) in addition to particles when using DualGrid | int | 0
load_balance.strategy | What strategy to use for load balancing Options are `KnapSack` and `SFC` | string | KnapSack
load_balance.weighting | What weighting function to use if using Knapsack load balancing Options are `ParticleRunTime`, `ParticleCount` and `CellCount` | string | ParticleRunTime
knapsack_nmax | Maximum number of grids per MPI process if using knapsack algorithm | int | 128
grid_pruning | Remove all covered grids from the base mesh; this may result in disjoined grids | bool | False

To allow a user to verify the breakdown of fluid grids created before running a full simulation, an input option, `mfix.only_print_grid_report` is supported. By default, it is `False`. When set to `True`, the run uses minimal memory to print the grid coverage report and exits immediately after that.

The following inputs are defined using the prefix `particles`:

| Description | Type | Default
--- | --- | --- | ---
max_grid_size_x | Maximum number of cells at level 0 in each grid in x-direction for grids in the ParticleBoxArray if dual_grid is true | Int | 32
max_grid_size_y | Maximum number of cells at level 0 in each grid in y-direction for grids in the ParticleBoxArray if dual_grid is true | Int | 32
max_grid_size_z | Maximum number of cells at level 0 in each grid in z-direction for grids in the ParticleBoxArray if dual_grid is true. | Int | 32