64 lines
1.8 KiB
HTML
64 lines
1.8 KiB
HTML
<HTML>
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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>
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</CENTER>
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<HR>
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<H3>nthreads command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>nthreads n
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</PRE>
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<UL><LI>n = # of threads to be used per MPI task
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>nthreads 1
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nthreads 6
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nthreads *
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Specify how many threads are to be used per MPI task in a hybrid MPI/multi-threading environment.processors are mapped as a 3d logical grid to the global
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simulation box.
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</P>
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<P>When this command has not been specified, LAMMPS will choose n according
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to the defaults of the threading environment, e.g. in OpenMP according to
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the OMP_NUM_THREADS environment variable or using all available processors
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if that is not set.
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</P>
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<P>For a package like LAMMPS, threading is typically not as efficient as
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a distributed data parallelization via domain decomposition using MPI
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message passing. Thus this keyword is mostly of use when MPI parallelization
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is becoming inefficient, e.g. when using a "slow" network (like GigE with
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TCP/IP) or when reaching the limit of scaling.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>This command cannot be used after the simulation box is defined by a
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<A HREF = "read_data.html">read_data</A> or <A HREF = "create_box.html">create_box</A> command.
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</P>
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<P>This command only has an effect and is only of use if LAMMPS was
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built with the "user-openmp" package included. See the <A HREF = "Section_start.html#2_3">Making
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LAMMPS</A> section for more info.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "processors.html">processors</A>
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</P>
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<P><B>Default:</B>
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</P>
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<PRE>nthreads *
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</PRE>
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<P>or in case multi-threading support is not compiled in:
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</P>
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<PRE>nthreads 1
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</PRE>
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</HTML>
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