MPI_Comm_split

--- Creates new communicators based on colors and keys

Input Parameters

comm: communicator (handle)

color: control of subset assignment (integer)

key: control of rank assigment (integer)

Output Parameter

newcomm: new communicator (handle)

Algorithm

The current algorithm used has quite a few (read: a lot of) inefficiencies

that can be removed. Here's what we do for now

1) A table is built of colors, and keys (has a next field also).
2) The tables of all processes are merged using MPI_Allreduce
3) Two contexts are allocated for all the comms to be created. These same two contexts can be used for all created communicators since the communicators will not overlap.
4) If the local process has a color of MPI_UNDEFINED, it can return a NULL comm.
5) The table entries that match the local process color are sorted by key/rank.
6) A group is created from the sorted list and a communicator is created with this group and the previously allocated contexts.

Synopsis


#include "mpi.h"
int MPI_Comm_split ( comm, color, key, comm_out )
MPI_Comm  comm;
int       color, key;
MPI_Comm *comm_out;

Location: comm_split.c