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rLAMMPS lammps
accelerate_opt.html
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<HTML>
<CENTER><A
HREF =
"Section_packages.html"
>
Previous Section
</A>
-
<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>
<P><A
HREF =
"Section_accelerate.html"
>
Return to Section accelerate overview
</A>
</P>
<H4>
5.3.6 OPT package
</H4>
<P>
The OPT package was developed by James Fischer (High Performance
Technologies), David Richie, and Vincent Natoli (Stone Ridge
Technologies). It contains a handful of pair styles whose compute()
methods were rewritten in C++ templated form to reduce the overhead
due to if tests and other conditional code.
</P>
<P>
Here is a quick overview of how to use the OPT package:
</P>
<UL><LI>
include the OPT package and build LAMMPS
<LI>
use OPT pair styles in your input script
</UL>
<P>
The last step can be done using the "-sf opt"
<A
HREF =
"Section_start.html#start_7"
>
command-line
switch
</A>
. Or the effect of the "-sf" switch
can be duplicated by adding a
<A
HREF =
"suffix.html"
>
suffix opt
</A>
command to your
input script.
</P>
<P><B>
Required hardware/software:
</B>
</P>
<P>
None.
</P>
<P><B>
Building LAMMPS with the OPT package:
</B>
</P>
<P>
Include the package and build LAMMPS:
</P>
<P>
To do this in one line, use the src/Make.py script, described in
<A
HREF =
"Section_start.html#start_4"
>
Section 2.4
</A>
of the manual. Type "Make.py
-h" for help. If run from the src directory, this command will create
src/lmp_opt using src/MAKE/Makefile.mpi as the starting
Makefile.machine:
</P>
<PRE>
Make.py -p opt -o opt file mpi
</PRE>
<P>
Or you can follow these steps:
</P>
<PRE>
cd lammps/src
make yes-opt
make machine
</PRE>
<P>
If you are using Intel compilers, then the CCFLAGS setting in
Makefile.machine needs to include "-restrict".
</P>
<P><B>
Run with the OPT package from the command line:
</B>
</P>
<P>
Use the "-sf opt"
<A
HREF =
"Section_start.html#start_7"
>
command-line switch
</A>
,
which will automatically append "opt" to styles that support it.
</P>
<PRE>
lmp_machine -sf opt -in in.script
mpirun -np 4 lmp_machine -sf opt -in in.script
</PRE>
<P><B>
Or run with the OPT package by editing an input script:
</B>
</P>
<P>
Use the
<A
HREF =
"suffix.html"
>
suffix opt
</A>
command, or you can explicitly add an
"opt" suffix to individual styles in your input script, e.g.
</P>
<PRE>
pair_style lj/cut/opt 2.5
</PRE>
<P><B>
Speed-ups to expect:
</B>
</P>
<P>
You should see a reduction in the "Pair time" value printed at the end
of a run. On most machines for reasonable problem sizes, it will be a
5 to 20% savings.
</P>
<P><B>
Guidelines for best performance:
</B>
</P>
<P>
None. Just try out an OPT pair style to see how it performs.
</P>
<P><B>
Restrictions:
</B>
</P>
<P>
None.
</P>
</HTML>
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