DeinoMPI

The Great and Terrible implementation of MPI-2

MPI_Graph_map

Maps process to graph topology information

int MPI_Graph_map(
  MPI_Comm comm_old,
  int nnodes,
  int *index,
  int *edges,
  int *newrank
);

Parameters

comm: [in] input communicator (handle)
nnodes: [in] number of graph nodes (integer)
index: [in] integer array specifying the graph structure, see MPI_GRAPH_CREATE
edges: [in] integer array specifying the graph structure
newrank: [out] reordered rank of the calling process; MPI_UNDEFINED if the calling process does not belong to graph (integer)

Remarks

Thread and Interrupt Safety

This routine is both thread- and interrupt-safe. This means that this routine may safely be used by multiple threads and from within a signal handler.

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. ierris 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 INTEGERin Fortran.

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_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 deprecated. 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.

MPI_SUCCESS: No error; MPI routine completed successfully.

MPI_ERR_TOPOLOGY: Invalid topology. Either there is no topology associated with this communicator, or it is not the correct type (e.g., MPI_CART when expecting MPI_GRAPH).

MPI_ERR_COMM: Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).

MPI_ERR_ARG: Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).

Example Code

The following sample code illustrates MPI_Graph_map.

#include "mpi.h"
#include <stdio.h>

int main( int argc, char *argv[] )
{
    int errs = 0;
    int newrank, merr, rank;
    int index[2], edges[2];

    MPI_Init( &argc, &argv );

    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    /* Graph map where there are no nodes for this process */
    MPI_Comm_set_errhandler( MPI_COMM_WORLD, MPI_ERRORS_RETURN );
    /* Here is a singleton graph, containing only the root process */
    index[0] = 0;
    edges[0] = 0;
    merr = MPI_Graph_map( MPI_COMM_WORLD, 1, index, edges, &newrank );
    if (merr) {
        errs++;
        printf( "Graph map returned an error\n" );fflush(stdout);
    }
    if (rank != 0 && newrank != MPI_UNDEFINED) {
        errs++;
        printf( "Graph map with no local nodes did not return MPI_UNDEFINED\n" );fflush(stdout);
    }

    MPI_Finalize();
    return errs;
}

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