Add option to have a separate MPI version of velociraptor

Adds new configure option --with-velociraptor-mpi so that an MPI version can be linked as well as a non-MPI one.

doc/RTD/source/VELOCIraptorInterface/stfwithswift.rst

@@ -5,13 +5,13 @@
 Configuring SWIFT with VELOCIraptor
 ===================================
 
-.. toctree::    
-   :maxdepth: 2    
-   :hidden:    
+.. toctree::
+   :maxdepth: 2
+   :hidden:
    :caption: Contents:
 
 In the following three paragraphs we will explain how to setup VELOCIraptor,
-how to compile it and how to compile SWIFT with VELOCIraptor. 
+how to compile it and how to compile SWIFT with VELOCIraptor.
 
 
 Setting up VELOCIraptor
@@ -25,15 +25,15 @@ VELOCIraptor. This can be done by cloning the repository on GitHub::
 The SWIFT interface is in the master branch of VELOCIraptor so nothing is more
 is needed besides fetching the latest version of the `NBodyLib` that the code
 relies upon::
-  
-  cd VELOCIraptor-STF 
+
+  cd VELOCIraptor-STF
   git submodule update --init --recursive
 
 To get VELOCIraptor working with SWIFT simply use::
 
   mkdir build
   cd build
-  cmake ../ -DVR_USE_HYDRO=ON -DVR_USE_SWIFT_INTERFACE=ON -DCMAKE_CXX_FLAGS="-fPIC" -DCMAKE_BUILD_TYPE=Release 
+  cmake ../ -DVR_USE_HYDRO=ON -DVR_USE_SWIFT_INTERFACE=ON -DCMAKE_CXX_FLAGS="-fPIC" -DCMAKE_BUILD_TYPE=Release
 
 The first parameter activates the processing of gas, stars and black holes. It
 can be omitted for simulations evolving only dark matter.
@@ -59,33 +59,38 @@ The next part is compiling SWIFT with VELOCIraptor and assumes you already
 downloaded SWIFT from the GitLab repository. This can be done by running
 
 .. code:: bash
-  
-  ./autogen.sh 
+
+  ./autogen.sh
   ./configure --with-velociraptor=/path/to/VELOCIraptor-STF/build/src
-  make 
+  make
 
 In which ``./autogen.sh`` only needs to be run once after the code is cloned
 from the GitLab_, and ``/path/to/`` is the path to the ``VELOCIraptor-STF``
 directory on your machine. Note that this path must be absolute (i.e. relative
-to ``/``. In general ``./configure`` can be run with other options as desired.
+to ``/``, if you want to run the MPI version of VELOCIraptor as well as a
+non-MPI one with the same version of SWIFT, then you will need to compile
+VELOCIraptor twice and create two builds, then use the
+``--with-velociraptor-mpi`` configure option to point to the MPI build and the
+``--with-velociraptor`` option to point at the non-MPI build.
+In general ``./configure`` can be run with other options as desired.
 After this we can run SWIFT with VELOCIraptor, but for this we first need to
 add several lines to the yaml file of our simulation
 
-    
+
 .. code:: YAML
 
-   StructureFinding:      
+   StructureFinding:
      config_file_name:     vrconfig_3dfof_subhalos_SO_hydro.cfg
      basename:             haloes
      scale_factor_first:   0.02
      delta_time:           1.02
 
-In which we specify the ``.cfg`` file that is used by VELOCIraptor and the 
-other parameters which SWIFT needs to use. In the case of 
+In which we specify the ``.cfg`` file that is used by VELOCIraptor and the
+other parameters which SWIFT needs to use. In the case of
 the Small Cosmological Volume DMO example we can run a simulation with halo
 finder as::
 
-  cd examples/SmallCosmoVolume_DM 
+  cd examples/SmallCosmoVolume_DM
   ../swift --cosmology --hydro --self-gravity --velociraptor --threads=8 small_cosmo_volume_dm.yml
 
 Which activates the VELOCIraptor interface.