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lammps/doc/_sources/fix_freeze.txt
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fix_freeze.txt
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.. index:: fix freeze
fix freeze command
==================
fix freeze/cuda command
=======================
Syntax
""""""
.. parsed-literal::
fix ID group-ID freeze
* ID, group-ID are documented in :doc:`fix <fix>` command
* freeze = style name of this fix command
Examples
""""""""
.. parsed-literal::
fix 2 bottom freeze
Description
"""""""""""
Zero out the force and torque on a granular particle. This is useful
for preventing certain particles from moving in a simulation. The
:doc:`granular pair styles <pair_gran>` also detect if this fix has been
defined and compute interactions between frozen and non-frozen
particles appropriately, as if the frozen particle has infinite mass.
A similar functionality for normal (point) particles can be obtained
using :doc:`fix setforce <fix_setforce>`.
----------
Styles with a *cuda* suffix are functionally the same as the
corresponding style without the suffix. They have been optimized to
run faster, depending on your available hardware, as discussed in
:doc:`Section_accelerate <Section_accelerate>` of the manual. The
accelerated styles take the same arguments and should produce the same
results, except for round-off and precision issues.
These accelerated styles are part of the USER-CUDA package. They are
only enabled if LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
use the :doc:`suffix <suffix>` command in your input script.
See :doc:`Section_accelerate <Section_accelerate>` of the manual for
more instructions on how to use the accelerated styles effectively.
----------
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.
This fix computes a global 3-vector of forces, which can be accessed
by various :ref:`output commands <howto_15>`. This is the
total force on the group of atoms before the forces on individual
atoms are changed by the fix. The vector values calculated by this
fix are "extensive".
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 GRANULAR package. It is only enabled if
LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
There can only be a single freeze fix defined. This is because other
the :doc:`granular pair styles <pair_gran>` treat frozen particles
differently and need to be able to reference a single group to which
this fix is applied.
Related commands
""""""""""""""""
:doc:`atom_style sphere <atom_style>`, :doc:`fix setforce <fix_setforce>`
**Default:** none
.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm
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