.. index:: Open MPI
.. _Open MPI:

Open MPI
========

Description
-----------

Open MPI is an open source MPI-2 and MPI-3 implementation that is developed and maintained by a consortium of academic, research, and industry partners.  Open MPI resulted from a merger of the code-bases from the FT-MPI, LA-MPI and LAM/MPI implementations and their respective communities and is actively developed.

User instructions
-----------------

Open MPI has been compiled for both the GNU and Intel 64-bit compiler families.  To use it, load the appropriate module:

.. code-block:: bash

    $ module load openmpi/2.1.1

Compiling MPI programs is best done using the MPI programs which act as wrappers around the desired compiler:

mpif90
    Fortran wrapper.
mpicc
    C wrapper
mpic++, mpiCC, mpicxx
    C++ wrapper

MPI-compiled programs should be run using the mpirun command, e.g. to run an MPI program on 2 processors:

.. code-block:: bash

    $ mpirun -np 2 /path/to/program.x

Documentation can be found via the manpages.

.. note::

    The majority of cluster workstations are good, but not suitable for highly-parallel calculations.  Please investigate the College's `HPC service <http://www3.imperial.ac.uk/ict/services/teachingandresearchservices/highperformancecomputing>`_ for running large-scale MPI calculations.  Open MPI is provided on the cluster for development purposes.

Source
------

http://www.openmpi.org.

License
-------

New BSD license (free, both in terms of speech and beer).

Admin notes
-----------

I compiled the GNU version using:

.. code-block:: bash

    $ ../openmpi-2.1.1/configure --prefix=/common/debian/9.1/Compiler/gcc/6.3/openmpi/openmpi-2.1.1 --disable-dlopen
    $ (make -j4 && make check) > make.log 2>&1 &
    $ make install

and the Intel version using:

.. code-block:: bash

    $ ../openmpi-2.1.1/configure --prefix=/common/debian/9.1/Compiler/intel/2017.4/openmpi/openmpi-2.1.1 --disable-dlopen CC=icc CXX=icpc F77=ifort FC=ifort
    $ (make -j4 && make check) > make.log 2>&1 &
    $ make install


Memchecker support can be enabled by adding ``--enable-debug --enable-memchecker`` to the configure command.  A version with this was previously installed (as an experiment when trying to track down a bug) but is not currently installed.  Please ask if this is of interest.

Note the additional flag at the configure stage: ``--disable-dlopen`` is in order to allow python to work with mpi. see https://github.com/jhedev/mpi_python for details of the issue.