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5.3.5 OPT package :h5

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.

Here is a quick overview of how to use the OPT package.  More details
follow.

make yes-opt
make mpi                               # build with the OPT package
Make.py -v -p opt -o mpi -a file mpi   # or one-line build via Make.py :pre

lmp_mpi -sf opt -in in.script                # run in serial
mpirun -np 4 lmp_mpi -sf opt -in in.script   # run in parallel :pre

[Required hardware/software:]

None.

[Building LAMMPS with the OPT package:]

The lines above illustrate how to build LAMMPS with the OPT package in
two steps, using the "make" command.  Or how to do it with one command
via the src/Make.py script, described in "Section
2.4"_Section_start.html#start_4 of the manual.  Type "Make.py -h" for
help.

Note that if you use an Intel compiler to build with the OPT package,
the CCFLAGS setting in your Makefile.machine must include "-restrict".
The Make.py command will add this automatically.

[Run with the OPT package from the command line:]

As in the lines above, use the "-sf opt" "command-line
switch"_Section_start.html#start_7, which will automatically append
"opt" to styles that support it.

[Or run with the OPT package by editing an input script:]

Use the "suffix opt"_suffix.html command, or you can explicitly add an
"opt" suffix to individual styles in your input script, e.g.

pair_style lj/cut/opt 2.5 :pre

[Speed-ups to expect:]

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.

[Guidelines for best performance:]

Just try out an OPT pair style to see how it performs.

[Restrictions:]

None.
