.. index:: fix sph/stationary

fix sph/stationary command
===========================

Syntax
""""""

.. parsed-literal::

   fix ID group-ID sph/stationary

* ID, group-ID are documented in :doc:`fix <fix>` command
* sph = style name of this fix command

Examples
""""""""

.. code-block:: 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 <USER/sph/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 :doc:`binary restart files <restart>`.  None of the :doc:`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 :doc:`output commands <Howto_output>`.
No parameter of this fix can be used with the *start/stop* keywords of
the :doc:`run <run>` command.  This fix is not invoked during :doc:`energy minimization <minimize>`.

Restrictions
""""""""""""

This fix is part of the USER-SPH package.  It is only enabled if
LAMMPS was built with that package.  See the :doc:`Build package <Build_package>` doc page for more info.

Related commands
""""""""""""""""

:doc:`fix sph <fix_sph>`

**Default:** none
