# fix sph/density/summation command

## Syntax

    fix ID group-ID sph/density/summation

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

## Examples

    fix density all sph/density/summation

## Description

Calculates the density field with the classic SPH-summation approach. The governing equation is given by:

rho<sub>a</sub> is the density of particle a, m is the mass and W<sub>ab</sub> denotes the interpolating kernel for the particle-particle distance r<sub>a</sub> - r<sub>b</sub>. The summation is over all particles b other than particle a.

Note

In the current version boundary or image particles are not implemented. Therefore, the density calculation in the vicinity to a wall will be wrong.

## 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/... (except fix sph/density/corr)

## Related commands

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

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).