[gmx-users] GROMACS 4.5.1 mdrun re-compile for MPI

[Adam Herbst]

Dear GROMACS users,
I successfully installed GROMACS 4.5.1 several months ago on a Mac Pro with
12 CPUs, and the "mdrun" command (not "mpirun mdrun_mpi") allows parallel
simulations--it automatically uses multiple processors, while the number of
processors can be manually specified as N with the flag "mdrun -nt N".  I
understand that this is a feature of GROMACS 4 and later.  Now I am making
minor changes to the mdrun source code, and I want to recompile such that
the parallel version of mdrun is updated with my changes.  But when I run:

  make mdrun (or just make)
  make install-mdrun (or just make install)

from the top-level source directory, the only executables that are updated
are the ones with the _mpi suffix, such as mdrun_mpi.  The version of mdrun
in src/kernel/ is updated, but this one has no -nt flag and cannot seem to
run on multiple processors.  And when I run

  mpirun -np N mdrun_mpi [options],

the same simulation is started separately on each processor, leading to a
crash.  If I use

  mpirun -np 1 -cpus-per-proc N mdrun_mpi [options],

I get an error message that this is not supported on my computer ("An
attempt to set processor affinity has failed").

I can't configure the input .tpr file for parallel because grompp doesn't
have the -np flag in GROMACS 4.

How can I update the parallel-capable "mdrun" executable with my changes?
Thanks in advance,

Adam
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