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# compute sph/rho/atom command¶

## Syntax¶

compute ID group-ID sph/rho/atom

• ID, group-ID are documented in compute command

• sph/rho/atom = style name of this compute command

## Examples¶

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 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 page for an overview of LAMMPS output options.

The per-atom vector values will be in mass/volume 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 page for more info.

none