# pair_style sph/rhosum command

## Syntax

``` LAMMPS
pair_style sph/rhosum Nstep
```

-   Nstep = timestep interval

## Examples

``` LAMMPS
pair_style sph/rhosum 10
pair_coeff * * 2.4
```

## Description

The sph/rhosum style computes the local particle mass density rho for
SPH particles by kernel function interpolation, every Nstep timesteps.

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

The following coefficients must be defined for each pair of atoms types
via the [pair_coeff](pair_coeff) command as in the examples above.

-   h (distance units)

------------------------------------------------------------------------

## Mixing, shift, table, tail correction, restart, rRESPA info

This style does not support mixing. Thus, coefficients for all I,J pairs
must be specified explicitly.

This style does not support the [pair_modify](pair_modify) shift, table,
and tail options.

This style does not write information to [binary restart
files](restart). Thus, you need to re-specify the pair_style and
pair_coeff commands in an input script that reads a restart file.

This style can only be used via the *pair* keyword of the [run_style
respa](run_style) command. It does not support the *inner*, *middle*,
*outer* keywords.

## Restrictions

This pair style 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

[pair_coeff](pair_coeff), pair_sph/taitwater

## Default

none