# compute sph/rho/atom command

## Syntax

    compute ID group-ID sph/rho/atom

-   ID, group-ID are documented in [compute](compute) command
-   sph/rho/atom = style name of this compute command

## Examples

``` LAMMPS
compute 1 all sph/rho/atom
```

## Description

Define a computation that calculates the per-atom SPH density for each
atom in a group, i.e. a Smooth-Particle Hydrodynamics density.

The SPH density is the mass density of an SPH particle, calculated by
kernel function interpolation using \"pair style sph/rhosum\".

See [this PDF guide](PDF/SPH_LAMMPS_userguide.pdf)\_ to using SPH in
LAMMPS.

The value of the SPH density will be 0.0 for atoms not in the specified
compute group.

## Output info

This compute calculates a per-atom vector, which can be accessed by any
command that uses per-atom values from a compute as input. See the
[Howto output](Howto_output) page for an overview of LAMMPS output
options.

The per-atom vector values will be in mass/volume [units](units).

## Restrictions

This compute is part of the SPH package. It is only enabled if LAMMPS
was built with that package. See the [Build package](Build_package) page
for more info.

## Related commands

[dump custom](dump)

## Default

none