# fix sph/density/continuity command

## Syntax

    fix ID group-ID sph/density/continuity

- ID, group-ID are documented in fix command
- sph/density/continuity = style name of this fix command

## Examples

    fix density all sph/density/continuity

## Description

Based on the continuity equation in the form

this fix calculates the density of each particle by the rule

where the summation is over all particles b other than particle a, m is the mass, v is the velocity, W<sub>ab</sub> is the interpolating kernel (documented in pair_style sph/artVisc/tensCorr) and &nabla;<sub>a</sub> is the gradient of W<sub>ab</sub>.

## Restart, fix_modify, output, run start/stop, minimize info

No information about this fix is written to binary restart files.

None of the fix_modify options are relevant to this fix.

No global scalar or vector or per_atom quantities are stored by this fix for access by various output commands.

No parameter of this fix can be used with the start/stop keywords of the run command.

This fix is not invoked during `energy minimization`.

## Restrictions

There can be only one fix sph/density.

## Related commands

pair_style sph/artVisc/tensCorr, fix sph/pressure, fix sph/density/corr

Default: none

(Liu and Liu, 2003) “Smoothed Particle Hydrodynamics: A Meshfree Particle Method”, G. R. Liu and M. B. Liu, World Scientific, p. 449 (2003).

(Monaghan, 1992) “Smoothed Particle Hydrodynamics”, J. J. Monaghan, Annu. Rev. Astron. Astrophys., 30, p. 543-574 (1992).