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# fix sph/stationary command¶

## Syntax¶

fix ID group-ID sph/stationary

• ID, group-ID are documented in fix command

• sph = style name of this fix command

## Examples¶

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 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. None of the 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. 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¶

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

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