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:
The last step can be done using the "-sf opt" command-line switch. Or the effect of the "-sf" switch can be duplicated by adding a suffix opt command to your input script.
Required hardware/software:
None.
Building LAMMPS with the OPT package:
Include the package and build LAMMPS:
cd lammps/src make yes-opt make machine
No additional compile/link flags are needed in your Makefile.machine in src/MAKE.
Run with the OPT package from the command line:
Use the "-sf opt" command-line switch, which will automatically append "opt" to styles that support it.
lmp_machine -sf opt -in in.script mpirun -np 4 lmp_machine -sf opt -in in.script
Or run with the OPT package by editing an input script:
Use the suffix opt 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
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:
None. Just try out an OPT pair style to see how it performs.
Restrictions:
None.