MPI is to me one of the greatest features to come to Stan and I think we are ready to make it happen soon. Here is my proposal for moving forward in a step-wise manner:
map_rectfunction should by now be final unless @Bob_Carpenter has any additional comments/concerns. The serial version should be included into stan-math asap. issue #686 on stan-math.
map_rectexposing to the Stan language. This requires the parser to handle the user supplied function in the usual special treatment. issue #2440 on stan
- Inclusion of MPI base system which includes only the basic mechanisms to send commands over the network. This should include a solution to test MPI code. Hence, I would expect that this pull also comes with changes to the test system to make it possible to test MPI enabled code.
- Inclusion of MPI enabled
- Inclusion of further parsers changes needed to make things work (boost macros to ensure that MPI communication can take place). This needs to go into Stan.
Any comments on the above would be appreciated; I hope these steps are clear in what they mean. Let me know if not or if we should split things up further.