.. index:: fix smd/adjust_dt

fix smd/adjust_dt command
=========================

Syntax
""""""

.. parsed-literal::

   fix ID group-ID smd/adjust_dt arg

* ID, group-ID are documented in :doc:`fix <fix>` command
* smd/adjust_dt = style name of this fix command
* arg = *s_fact*
.. parsed-literal::

     *s_fact* = safety factor



Examples
""""""""

.. parsed-literal::

   fix 1 all smd/adjust_dt 0.1

Description
"""""""""""

The fix calculates a new stable time increment for use with the SMD time integrators.

The stable time increment is based on multiple conditions. For the SPH pair styles, a 
CFL criterion (Courant, Friedrichs & Lewy, 1928) is evaluated, which determines the the speed of
sound cannot propagate further than a typical spacing between particles within a single time step to ensure
no information is lost. For the contact pair styles, a linear analysis of the pair potential determines a
stable maximum time step.

This fix inquires the minimum stable time increment across all particles contained in the group for which this
fix is defined. An additional safety factor *s_fact* is applied to the time increment.

See `this PDF guide <USER/smd/SMD_LAMMPS_userguide.pdf>`_ to use Smooth Mach Dynamics in LAMMPS.

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

Currently, no part of USER-SMD supports restarting nor minimization.

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


This fix is part of the USER-SMD package.  It is only enabled if
LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>`
section for more info.

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

:doc:`smd/tlsph_dt <compute_smd_tlsph_dt>`

**Default:** none


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm