# compute property/grid command

## Syntax

    compute ID group-ID property/grid Nx Ny Nz input1 input2 ...

-   ID, group-ID are documented in [compute](compute) command

-   property/grid = style name of this compute command

-   Nx, Ny, Nz = grid size in each dimension

-   input1,etc = one or more attributes

        attributes = id, ix, iy, iz, x, y, z, xs, ys, zs, xc, yc, zc, xsc, ysc, zsc
          id = ID of grid cell, x fastest, y next, z slowest
          ix,iy,iz = grid indices in each dimension (1 to N inclusive)
          x,y,z = coords of lower left corner of grid cell
          xs,ys,zs = scaled coords of lower left corner of grid cell (0.0 to 1.0)
          xc,yc,zc = coords of center point of grid cell
          xsc,ysc,zsc = scaled coords of center point of grid cell (0.0 to 1.0)

## Examples

``` LAMMPS
compute 1 all property/grid id ix iy iz
compute 1 all property/grid id xc yc zc
```

## Description

Define a computation that stores the specified attributes of a
distributed grid. In LAMMPS, distributed grids are regular 2d or 3d
grids which overlay a 2d or 3d simulation domain. Each processor owns
the grid cells whose center points lie within its subdomain. See the
[Howto grid](Howto_grid) doc page for details of how distributed grids
can be defined by various commands and referenced.

This compute stores the specified attributes of grids as per-grid data
so they can be accessed by other [output commands](Howto_output) such as
[dump grid](dump).

*Nx*, *Ny*, and *Nz* define the size of the grid. For a 2d simulation
*Nz* must be 1. When this compute is used by [dump grid](dump), to
output per-grid values from other computes of fixes, the grid size
specified for this command must be consistent with the grid sizes used
by the other commands.

The *id* attribute stores the grid ID for each grid cell. For a global
grid of size Nx by Ny by Nz (in 3d simulations) the grid IDs range from
1 to Nx\*Ny\*Nz. They are ordered with the X index of the 3d grid
varying fastest, then Y, then Z slowest. For 2d grids (in 2d
simulations), the grid IDs range from 1 to Nx\*Ny, with X varying
fastest and Y slowest.

The *ix*, *iy*, *iz* attributes are the indices of a grid cell in each
dimension. They range from 1 to Nx inclusive in the X dimension, and
similar for Y and Z.

The *x*, *y*, *z* attributes are the coordinates of the lower left
corner point of each grid cell.

The *xs*, *ys*, *zs* attributes are also coordinates of the lower left
corner point of each grid cell, except in scaled coordinates, where the
lower-left corner of the entire simulation box is (0,0,0) and the upper
right corner is (1,1,1).

The *xc*, *yc*, *zc* attributes are the coordinates of the center point
of each grid cell.

The *xsc*, *ysc*, *zsc* attributes are also coordinates of the center
point each grid cell, except in scaled coordinates, where the lower-left
corner of the entire simulation box is (0,0,0) and the upper right
corner is (1,1,1).

For [triclinic simulation boxes](Howto_triclinic), the grid point
coordinates for (x,y,z) and (xc,yc,zc) will reflect the triclinic
geometry. For (xs,yz,zs) and (xsc,ysc,zsc), the coordinates are the same
for orthogonal versus triclinic boxes.

## Output info

This compute calculates a per-grid vector or array depending on the
number of input values. The length of the vector or number of array rows
(distributed across all processors) is Nx \* Ny \* Nz. For access by
other commands, the name of the single grid produced by this command is
\"grid\". The name of its per-grid data is \"data\".

The (x,y,z) and (xc,yc,zc) coordinates are in distance [units](units).

## Restrictions

For 2d simulations, the attributes which refer to the Z dimension cannot
be used.

## Related commands

[dump grid](dump)

## Default

none