Updated alternate MPI implementation that does not use spawn.

README.rst

@@ -177,6 +177,7 @@ Argument name          Type      Description
 ``-restart``           integer   model number to start/restart simulation from. It would typically be used to restart a series of models from a specific model number, with the ``-n`` argument, e.g. to restart from A-scan 45 when creating a B-scan with 60 traces: ``(gprMax)$ python -m gprMax user_models/cylinder_Bscan_2D.in -n 15 -restart 45``
 ``-task``              integer   task identifier (model number) when running simulation as a job array on `Open Grid Scheduler/Grid Engine <http://gridscheduler.sourceforge.net/index.html>`_. For further details see the `parallel performance section of the User Guide <http://docs.gprmax.com/en/latest/openmp_mpi.html>`_
 ``-mpi``               integer   number of Message Passing Interface (MPI) tasks, i.e. master + workers, for MPI task farm. This option is most usefully combined with ``-n`` to allow individual models to be farmed out using a MPI task farm, e.g. to create a B-scan with 60 traces and use MPI to farm out each trace: ``(gprMax)$ python -m gprMax user_models/cylinder_Bscan_2D.in -n 60 -mpi 61``. For further details see the `parallel performance section of the User Guide <http://docs.gprmax.com/en/latest/openmp_mpi.html>`_
+``--mpi-no-spawn``     flag      use MPI task farm without spawn mechanism. For further details see the `parallel performance section of the User Guide <http://docs.gprmax.com/en/latest/openmp_mpi.html>`_
 ``-benchmark``         flag      switch on benchmarking mode. This can be used to benchmark the threading (parallel) performance of gprMax on different hardware. For further details see the `benchmarking section of the User Guide <http://docs.gprmax.com/en/latest/benchmarking.html>`_
 ``--geometry-only``    flag      build a model and produce any geometry views but do not run the simulation, e.g. to check the geometry of a model is correct: ``(gprMax)$ python -m gprMax user_models/heterogeneous_soil.in --geometry-only``
 ``--geometry-fixed``   flag      run a series of models where the geometry does not change between models, e.g. a B-scan where *only* the position of simple sources and receivers, moved using ``#src_steps`` and ``#rx_steps``, changes between models.