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# compute smd/rho command

## Syntax

    compute ID group-ID smd/rho

- ID, group-ID are documented in compute command

- smd/rho = style name of this compute command

## Examples

    compute 1 all smd/rho

## Description

Define a computation that calculates the per-particle mass density. The mass density is the mass of a particle which is constant during the course of a simulation, divided by its volume, which can change due to mechanical deformation.

See this PDF guide to use Smooth Mach Dynamics in LAMMPS.

## Output info

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

The per-particle values will be in units of mass over volume.

## Restrictions

This compute is part of the MACHDYN package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

## Related commands

compute smd/vol

## Default

none