:doc:`Return to Section accelerate overview <Section_accelerate>`

5.OPT package
-------------

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.

.. parsed-literal::

   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

.. parsed-literal::

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

**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 :ref:`Section 2.4 <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" :ref:`command-line switch <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 :doc:`suffix opt <suffix>` command, or you can explicitly add an
"opt" suffix to individual styles in your input script, e.g.

.. parsed-literal::

   pair_style lj/cut/opt 2.5

**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.


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Section_commands.html#comm