MPI_COMM_SPLIT(3)MPI_COMM_SPLIT(3)NAMEMPI_Comm_split - Creates new communicators based on colors and keys
SYNOPSIS
C:
#include <mpi.h>
int MPI_Comm_split ( comm, color, key, comm_out )
MPI_Comm comm;
int color, key;
MPI_Comm *comm_out;
C++:
#include <mpi.h>
Intracomm Intracomm::Split(
int color,
int key) const
Fortran:
INCLUDE "mpif.h" (or USE MPI)
INTEGER comm, color, key, newcomm, ierror
CALL MPI_COMM_SPLIT(comm, color, key, newcomm,
ierror)
STANDARDS
This release implements the MPI 1.2 standard, as documented by the MPI
Forum in the spring 1997 release of MPI: A Message Passing Interface
Standard.
DESCRIPTION
The MPI_Comm_split routine creates new communicators based on colors and
keys. This routine accepts the following parameters:
comm Specifies the communicator. (handle)
color Specifies the control of subset assignment. color must be
nonnegative or MPI_UNDEFINED. (nonnegative integer)
key Specifies the control of rank assignment. (integer)
comm_out Returns a new communicator. (handle)
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MPI_COMM_SPLIT(3)MPI_COMM_SPLIT(3)
ierror Specifies the return code value for successful completion,
which is in MPI_SUCCESS. MPI_SUCCESS is defined in the mpif.h
file.
NOTES
The algorithm that is used for creating new communicators based on colors
and keys is as follows:
1. A table of colors and keys is built (has a next field also).
2. The MPI_Allreduce(3) routine is used to merge the tables of all
processes.
3. Two contexts are allocated for all of the communicators to be
created. These same two contexts can be used for all created
communicators because the communicators will not overlap.
4. If the local process has a color of MPI_UNDEFINED, it can return a
null communicator.
5. The table entries that match the local process color are sorted by
key and rank.
6. A group is created from the sorted list and a communicator is
created with this group and the previously allocated contexts.
Note: This algorithm contains inefficiencies that can be removed.
SEE ALSOMPI_Allreduce(3)
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