[gmx-users] How can I tell whether or not Gromacs was compiled with MPI?

[Andrew DeYoung]

Hi, 

I am running Gromacs version 4.5.5.  However, I did not compile it myself;
the system administrator did many months ago.  I have been running
"standard" MD simulations (i.e., no replica exchange) over the 24 cores that
are available on the node.  To run "standard" MD, I just call mdrun directly
-- without referencing MPI or mpirun (at least not explicitly) -- using a
command like this: 

mdrun -v -s topol.tpr -nt 24

>From looking at the old release notes, it looks like this "thread-based
parallelization" was introduced sometime in version 4.5 (maybe from the
beginning of version 4.5?).  As the page
http://www.gromacs.org/About_Gromacs/Release_Notes/Versions_4.5.x says,

"Running on a multi-core node now uses thread-based parallelization to
automatically spawn the optimum number of threads in the default build. MPI
is now only required for parallelization over the network."

Now, however, I want to run replica exchange simulations.  I have no
experience with such simulations, but the page
http://www.gromacs.org/Documentation/How-tos/REMD says:

"REMD with any version of GROMACS requires mdrun compiled with MPI (i.e. not
threading), and that the number of processors be a multiple of the number of
replicas."

But, my question is, how can I tell whether Gromacs was compiled with MPI?
Probably it was not compiled with MPI, since I am using threading, but how
can I be sure?

Thanks so much for your time!

Andrew DeYoung
Carnegie Mellon University