HP-MPI User's Guide (11th Edition)

Frequently asked questions
General
Appendix D 297
ANSWER: MPI_ROOT is an environment variable that HP-MPI (mpirun)
uses to determine where HP-MPI is installed and therefore which
executables and libraries to use. It is particularly helpful when you have
multiple versions of HP-MPI installed on a system. A typical invocation
of HP-MPI on systems with multiple MPI_ROOTs installed is:
% setenv MPI_ROOT /scratch/test-hp-mpi-2.2.5/
% $MPI_ROOT/bin/mpirun ...
Or
% export MPI_ROOT=/scratch/test-hp-mpi-2.2.5
% $MPI_ROOT/bin/mpirun ...
If you only have one copy of HP-MPI installed on the system and it is in
/opt/hpmpi or /opt/mpi, then you do not need to set MPI_ROOT.
For Windows, see the Windows FAQ section.
QUESTION: Can you confirm that HP-MPI is include-file-compatible with
MPICH?
ANSWER
: HP-MPI can be used in what we refer to as MPICH
compatibility mode. In general, object files built with HP-MPI’s MPICH
mode can be used in an MPICH application, and conversely object files
built under MPICH can be linked into an HP-MPI application using
MPICH mode. However, using MPICH compatibility mode to produce a
single executable to run under both MPICH and HP_MPI will be more
problematic and is not recommended. Refer to “MPICH object
compatibility for HP-UX and Linux” on page 62 for more information.