Add datatype for MPI Bcast.

Author: sidward

sigpy/backend.py

@@ -265,17 +265,21 @@ def reduce(self, input, root=0):
             else:
                 self.mpi_comm.Reduce(cpu_input, None, root=root)
 
-    def bcast(self, input, root=0):
+    def bcast(self, input, root=0, datatype=None):
         """Broadcast from root to other nodes.
 
         Args:
             input (array): input array.
             root (int): root node rank.
+            datatype (int): MPI datatype for broadcasting.
 
         """
+        if config.mpi4py_enabled:
+            datatype = MPI.COMPLEX
+
         if self.size > 1:
             cpu_input = to_device(input, cpu_device)
-            self.mpi_comm.Bcast(cpu_input, root=root)
+            self.mpi_comm.Bcast((cpu_input, datatype), root=root)
             copyto(input, cpu_input)
 
     def gatherv(self, input, root=0):