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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
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<H3>fix gpu command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>fix ID group-ID gpu mode first last split
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
<LI>gpu = style name of this fix command
<LI>mode = force or force/neigh
<LI>first = ID of first GPU to be used on each node
<LI>last = ID of last GPU to be used on each node
<LI>split = fraction of particles assigned to the GPU
</UL>
<P><B>Examples:</B>
</P>
<PRE>fix 0 all gpu force 0 0 1.0
fix 0 all gpu force 0 0 0.75
fix 0 all gpu force/neigh 0 0 1.0
fix 0 all gpu force/neigh 0 1 -1.0
</PRE>
<P><B>Description:</B>
</P>
<P>Select and initialize GPUs to be used for acceleration and configure
GPU acceleration in LAMMPS. This fix is required in order to use
any style with GPU acceleration. The fix must be the first fix
specified for a run or an error will be generated. The fix will not have an
effect on any LAMMPS computations that do not use GPU acceleration, so there
should not be any problems with specifying this fix first in input scripts.
</P>
<P>The <I>mode</I> setting specifies where neighbor list calculations will be
performed. If <I>mode</I> is force, neighbor list calculation is performed
on the CPU. If <I>mode</I> is force/neigh, neighbor list calculation is
performed on the GPU. GPU neighbor list calculation currently cannot
be used with a triclinic box. GPU neighbor list calculation currently
cannot be used with <A HREF = "pair_hybrid.html">hybrid</A> pair styles. GPU
neighbor lists are not compatible with styles that are not
GPU-enabled. When a non-GPU enabled style requires a neighbor list,
it will also be built using CPU routines. In these cases, it will
typically be more efficient to only use CPU neighbor list builds.
</P>
<P>The <I>first</I> and <I>last</I> settings specify the GPUs that will be used for
simulation. On each node, the GPU IDs in the inclusive range from
<I>first</I> to <I>last</I> will be used.
</P>
<P>The <I>split</I> setting can be used for load balancing force calculation
work between CPU and GPU cores in GPU-enabled pair styles. If
0<<I>split</I><1.0, a fixed fraction of particles is offloaded to the GPU
while force calculation for the other particles occurs simulataneously
on the CPU. If <I>split</I><0, the optimal fraction (based on CPU and GPU
timings) is calculated every 25 timesteps. If <I>split</I>=1.0, all force
calculations for GPU accelerated pair styles are performed on the
GPU. In this case, <A HREF = "pair_hybrid.html">hybrid</A>, <A HREF = "bond_style.html">bond</A>,
<A HREF = "angle_style.html">angle</A>, <A HREF = "dihedral_style.html">dihedral</A>,
<A HREF = "improper_style.html">improper</A>, and <A HREF = "kspace_style.html">long-range</A>
calculations can be performed on the CPU while the GPU is performing
force calculations for the GPU-enabled pair style.
</P>
<P>In order to use GPU acceleration, a GPU enabled style must be selected
in the input script in addition to this fix. Currently, this is
limited to a few <A HREF = "pair_style.html">pair styles</A> and the PPPM <A HREF = "kspace_style.html">kspace
style</A>.
</P>
<P>See <A HREF = "doc/Section_accerate.html">this section</A> of the manual for more
details about using the GPU package.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</P>
<P>This fix is part of the "gpu" package. It is only enabled if LAMMPS
was built with that package. See the <A HREF = "Section_start.html#2_3">Making
LAMMPS</A> section for more info.
</P>
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
are relevant to this fix.
</P>
<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
the <A HREF = "run.html">run</A> command.
</P>
<P><B>Restrictions:</B>
</P>
<P>The fix must be the first fix specified for a given run. The
force/neigh <I>mode</I> should not be used with a triclinic box or
<A HREF = "pair_hybrid.html">hybrid</A> pair styles.
</P>
<P>The <I>split</I> setting must be positive when using
<A HREF = "pair_hybrid.html">hybrid</A> pair styles.
</P>
<P>Currently, group-ID must be all.
</P>
<P><B>Related commands:</B> none
</P>
<P><B>Default:</B> none
</P>
</HTML>
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