Feature pass MPI comm from Python script to AMReX during initialization (#2034)

* Added functionality to pass mpi comm from python script to amrex during initialization

* Fixed missing _ in MPI._sizeof()

* Added functions to get the current processor's rank and total number of processors

* Renamed MPI_Comm to _MPI_Comm_type and defined _MPI_Comm_type in except statement

* Updated comment to explain why mpi4py needs to be imported before loading libwarpx

* Removed ifdef flags that prevent amrex_init_with_inited_mpi from being declared when MPI is off

* Changed amrex_init_with_inited_mpi to be declared even when not using mpi, but will be defined to be functionally the same as amrex_init

* Defined MPI = None to signify whether MPI is used, to add another check when initializing amrex

* Changed ifdef blocks in WarpXWrappers.cpp/h to fix compile errors.
Added ifdef block to conditionally declare amrex_init_with_inited_mpi in WarpXWrappers.h to prevent compile error when not using MPI. Removed ifdef block to declare/define same function in WarpXWrappers.cpp since function needs to be declared even when MPI is not used, but will never be called in that case.

* Changed BL_USE_MPI to AMREX_USE_MPI and removed incorrect MPI=None statement

* Changed BL_USE_MPI to AMREX_USE_MPI

* Added test to verify correct passing of MPI communicator to amrex

* Added ability to pass mpi_comm to sim.step

* Change test to check for differeing outputs when passed different inputs

* Removed obsolete comments refactored program to use more shared code

* Refactored comments

* Updated description to match test

* Removed unecessary imports and updated comments

1 files changed, 2 insertions, 2 deletions

diff --git a/Python/pywarpx/WarpX.py b/Python/pywarpx/WarpX.py
index dc09ba241..73106cf62 100644
--- a/Python/pywarpx/WarpX.py
+++ b/Python/pywarpx/WarpX.py
@@ -68,10 +68,10 @@ class WarpX(Bucket):
 
         return argv
 
-    def init(self):
+    def init(self, mpi_comm=None):
         from . import wx
         argv = ['warpx'] + self.create_argv_list()
-        wx.initialize(argv)
+        wx.initialize(argv, mpi_comm=mpi_comm)
 
     def evolve(self, nsteps=-1):
         from . import wx