~~NOTOC~~
====== Compiling potfit with MPI parallelization ======
----

//potfit// does support all common MPI implementations for parallel execution. While the build process for an MPI-enabled build is almost the same as a regular build, there are some minor differences you should be aware of.

===== Basics =====

In order to enable MPI support in //potfit// the ''--enable-mpi'' command line option needs to be specified. It will always be assumed that there is an ''mpicc'' command which knows how to handle the current environment properly. 

<wrap round warning 595px center>
When using ''--enable-mpi'' you cannot specify a compiler with the ''--check-c-compiler'' flag!
</wrap>

A command to compile //potfit// with MPI support might look like this:

<code>./waf configure -i pair -m apot --enable-mpi</code>

Usually you should see output similar to this:

<code>
Checking for 'icc' (C compiler)          : not found 
Checking for 'clang' (C compiler)        : not found 
Checking for 'gcc' (C compiler)          : mpicc 
</code>

All enabled options will also be listed on the summary of the configuration stage:

<code>
potfit has been configured with the following options:
potential model      = apot
interaction          = pair
math library         = mkl
options              = mpi
</code>

===== Selecting the MPI compiler =====

The selection of the MPI compiler depends on your MPI implementation. For [[https://www.open-mpi.org/|Open MPI]] this behavior is controlled through environment variables, like ''OMPI_CC'', ''OMPI_CFLAGS'' and ''OMPI_LDFLAGS''.

To switch the compiler you can use this command (OpenMPI):


<code>OMPI_CC="clang" ./waf configure -i pair -m apot --enable-mpi</code>

Checking the output, you should see that the ''mpicc'' command has now been identified as a clang compiler:

<code>
Checking for 'icc' (C compiler)          : not found 
Checking for 'clang' (C compiler)        : mpicc
</code>

To make sure the same value of the environment variables are used for all steps of the //potfit// compilation process please export the variable using you shell.