MPI_Comm_split

split a communicator

Synopsis

int MPI_Comm_split(MPI_Comm comm, int color, int key, MPI_Comm *newcomm)

Arguments

MPI_Comm comm
communicator
int color
color
int key
key
MPI_Comm *newcomm
new communicator

Notes

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

Algorithm

  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

Errors

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_Errhandler_set; 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.

MPI_SUCCESS
No error; MPI routine completed successfully.

Location:comm_split.c