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Appendix
========
.. _python-mpi:
MPI-enabled Python interpreter
------------------------------
.. warning::
These days it is no longer required to use the MPI-enabled Python
interpreter in most cases, and, therefore, it is not built by
default anymore because it is too difficult to reliably build a
Python interpreter across different distributions. If you know
that you still **really** need it, see below on how to use the
``build_exe`` and ``install_exe`` commands.
Some MPI-1 implementations (notably, MPICH 1) **do require** the
actual command line arguments to be passed at the time
:c:func:`MPI_Init()` is called. In this case, you will need to use a
re-built, MPI-enabled, Python interpreter binary executable. A basic
implementation (targeting Python 2.X) of what is required is shown
below:
.. sourcecode:: c
#include <Python.h>
#include <mpi.h>
int main(int argc, char *argv[])
{
int status, flag;
MPI_Init(&argc, &argv);
status = Py_Main(argc, argv);
MPI_Finalized(&flag);
if (!flag) MPI_Finalize();
return status;
}
The source code above is straightforward; compiling it should also
be. However, the linking step is more tricky: special flags have to be
passed to the linker depending on your platform. In order to alleviate
you for such low-level details, *MPI for Python* provides some
pure-distutils based support to build and install an MPI-enabled
Python interpreter executable::
$ cd mpi4py-X.X.X
$ python setup.py build_exe [--mpi=<name>|--mpicc=/path/to/mpicc]
$ [sudo] python setup.py install_exe [--install-dir=$HOME/bin]
After the above steps you should have the MPI-enabled interpreter
installed as :file:`{prefix}/bin/python{X}.{X}-mpi` (or
:file:`$HOME/bin/python{X}.{X}-mpi`). Assuming that
:file:`{prefix}/bin` (or :file:`$HOME/bin`) is listed on your
:envvar:`PATH`, you should be able to enter your MPI-enabled Python
interactively, for example::
$ python2.7-mpi
Python 2.7.8 (default, Nov 10 2014, 08:19:18)
[GCC 4.9.2 20141101 (Red Hat 4.9.2-1)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.executable
'/usr/bin/python2.7-mpi'
>>>
.. _building-mpi:
Building MPI from sources
-------------------------
In the list below you have some executive instructions for building
some of the open-source MPI implementations out there with support for
shared/dynamic libraries on POSIX environments.
+ *MPICH* ::
$ tar -zxf mpich-X.X.X.tar.gz
$ cd mpich-X.X.X
$ ./configure --enable-shared --prefix=/usr/local/mpich
$ make
$ make install
+ *Open MPI* ::
$ tar -zxf openmpi-X.X.X tar.gz
$ cd openmpi-X.X.X
$ ./configure --prefix=/usr/local/openmpi
$ make all
$ make install
+ *MPICH 1* ::
$ tar -zxf mpich-X.X.X.tar.gz
$ cd mpich-X.X.X
$ ./configure --enable-sharedlib --prefix=/usr/local/mpich1
$ make
$ make install
Perhaps you will need to set the :envvar:`LD_LIBRARY_PATH`
environment variable (using :command:`export`, :command:`setenv` or
what applies to your system) pointing to the directory containing the
MPI libraries . In case of getting runtime linking errors when running
MPI programs, the following lines can be added to the user login shell
script (:file:`.profile`, :file:`.bashrc`, etc.).
- *MPICH* ::
MPI_DIR=/usr/local/mpich
export LD_LIBRARY_PATH=$MPI_DIR/lib:$LD_LIBRARY_PATH
- *Open MPI* ::
MPI_DIR=/usr/local/openmpi
export LD_LIBRARY_PATH=$MPI_DIR/lib:$LD_LIBRARY_PATH
- *MPICH 1* ::
MPI_DIR=/usr/local/mpich1
export LD_LIBRARY_PATH=$MPI_DIR/lib/shared:$LD_LIBRARY_PATH:
export MPICH_USE_SHLIB=yes
.. warning::
MPICH 1 support for dynamic libraries is not completely
transparent. Users should set the environment variable
:envvar:`MPICH_USE_SHLIB` to ``yes`` in order to avoid link
problems when using the :program:`mpicc` compiler wrapper.
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