# fix_modify AtC poisson_solver command

## Syntax

    fix_modify <AtC fixID> poisson_solver mesh create <nx> <ny> <nz> <region-ID> <f|p> <f|p> <f|p>

-   AtC fixID = ID of [fix atc](fix_atc) instance
-   poisson_solver = name of the AtC sub-command
-   *nx* *ny* *nz* = number of elements in x, y, and z
-   region-id = id of region to be meshed
-   *f* or *p* = periodicity flags for x, y, and z

## Examples

``` LAMMPS
fix_modify AtC poisson_solver mesh create 10 1 1 feRegion p p p
```

## Description

Creates a uniform mesh in a rectangular region.

## Restrictions

Creates only uniform rectangular grids in rectangular regions.

## Related AtC commands

-   [fix_modify AtC command overview](atc_fix_modify)

## Default

None.