int MPI_Comm_split(MPI_Comm comm, int color, int key, MPI_Comm *newcomm)
All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.
1. Use MPI_Allgather to get the color and key from each process 2. Count the number of processes with the same color; create a communicator with that many processes. If this process has MPI_UNDEFINED as the color, create a process with a single member. 3. Use key to order the ranks 4. Set the VCRs using the ordered key values
All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecatd. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.
Location:comm_split.c