This generates an MPI parallelized executable with mpiCC (based on g++)
for running a large grid.

to build enter
make
at the command prompt, to build debug do
make debug

add "-j n" where n is the number of threads to use in the build.

This will not work on a Mac, since it uses mpiCC which is misinterpreted as
mpicc on the Mac file system.  Use the sys_mpi_mac directory below this.