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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>
<HR>
<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><I>mode</I> 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><I>first</I> and <I>last</I> 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><I>split</I> 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>More details about these settings and various possible hardware
configuration are in <A HREF = "Section_start.html#2_8">this section</A> of the
manual.
</P>
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
</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><I>split</I> 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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