# fix sph/stationary command

## Syntax

    fix ID group-ID sph/stationary

-   ID, group-ID are documented in [fix](fix) command
-   sph = style name of this fix command

## Examples

``` LAMMPS
fix 1 boundary sph/stationary
```

## Description

Perform time integration to update internal energy and local density,
but not position or velocity for atoms in the group each timestep. This
fix is needed for SPH simulations to correctly time-integrate fixed
boundary particles which constrain a fluid to a given region in space.
SPH stands for Smoothed Particle Hydrodynamics.

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

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

No information about this fix is written to [binary restart
files](restart). None of the [fix_modify](fix_modify) options are
relevant to this fix. No global or per-atom quantities are stored by
this fix for access by various [output commands](Howto_output). No
parameter of this fix can be used with the *start/stop* keywords of the
[run](run) command. This fix is not invoked during [energy
minimization](minimize).

## Restrictions

This fix 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

[fix sph](fix_sph)

## Default

none