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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>processors command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>processors Px Py Pz
</PRE>
<UL><LI>Px,Py,Pz = # of processors in each dimension of a 3d grid
</UL>
<P><B>Examples:</B>
</P>
<PRE>processors 2 4 4
</PRE>
<P><B>Description:</B>
</P>
<P>Specify how processors are mapped as a 3d logical grid to the global
simulation box.
</P>
<P>When this command has not been specified, LAMMPS will choose Px, Py,
Pz based on the dimensions of the global simulation box so as to
minimize the surface/volume ratio of each processor's sub-domain.
</P>
<P>Since LAMMPS does not load-balance by changing the grid of 3d
processors on-the-fly, this command should be used to override the
LAMMPS default if it is known to be sub-optimal for a particular
problem. For example, a problem where the atom's extent will change
dramatically over the course of the simulation.
</P>
<P>The product of Px, Py, Pz must equal P, the total # of processors
LAMMPS is running on. If multiple partitions are being used then P is
the number of processors in this partition; see <A HREF = "Section_start.html#2_6">this
section</A> for an explanation of the -partition
command-line switch.
</P>
<P>If P is large and prime, a grid such as 1 x P x 1 will be required,
which may incur extra communication costs.
</P>
<P><B>Restrictions:</B>
</P>
<P>This command cannot be used after the simulation box is defined by a
<A HREF = "read_data.html">read_data</A> or <A HREF = "create_box.html">create_box</A> command.
It can be used before a restart file is read to change the 3d
processor grid from what is specified in the restart file.
</P>
<P><B>Related commands:</B> none
</P>
<P><B>Default:</B>
</P>
<P>LAMMPS chooses Px, Py, Pz
</P>
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