int MPI_Topo_test(
  MPI_Comm comm,
  int *topo_type
);

Parameters

comm

[in] communicator (handle)

top_type

[out] topology type of communicator comm (integer). If the communicator has no associated topology, returns MPI_UNDEFINED.

Remarks

The function MPI_TOPO_TEST returns the type of topology that is assigned to a communicator.

The output value status is one of the following:
[ MPI_GRAPH] graph topology
[ MPI_CART] cartesian topology
[ MPI_UNDEFINED] no topology

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 objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in 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_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).

See Also

Example Code

The following sample code illustrates MPI_Topo_test.

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

int main( int argc, char *argv[] )
{
    int errs = 0, i, k;
        int dims[2], periods[2], wsize;
    int outdims[2], outperiods[2], outcoords[2];
    int topo_type;
    int *index, *edges, *outindex, *outedges;
    MPI_Comm comm1, comm2;

    MPI_Init( &argc, &argv );
    MPI_Comm_size( MPI_COMM_WORLD, &wsize );

    /* Create a cartesian topology, get its characteristics, then
        dup it and check that the new communicator has the same properties */
    dims[0] = dims[1] = 0;
    MPI_Dims_create( wsize, 2, dims );
    periods[0] = periods[1] = 0;
    MPI_Cart_create( MPI_COMM_WORLD, 2, dims, periods, 0, &comm1 );
    MPI_Comm_dup( comm1, &comm2 );
    MPI_Topo_test( comm2, &topo_type );
    if (topo_type != MPI_CART) {
        errs++;
        printf( "Topo type of duped cart was not cart\n" );fflush(stdout);
    }
    else {
        MPI_Cart_get( comm2, 2, outdims, outperiods, outcoords );
        for (i=0; i<2; i++) {
            if (outdims[i] != dims[i]) {
                errs++;
                printf( "%d = outdims[%d] != dims[%d] = %d\n", outdims[i], i, i, dims[i] );fflush(stdout);
            }
            if (outperiods[i] != periods[i]) {
                errs++;
                printf( "%d = outperiods[%d] != periods[%d] = %d\n", outperiods[i], i, i, periods[i] );fflush(stdout);
            }
        }
    }
    MPI_Comm_free( &comm2 );
    MPI_Comm_free( &comm1 );

    /* Now do the same with a graph topology */
    if (wsize >= 3) {
        index = (int*)malloc(wsize * sizeof(int) );
        edges = (int*)malloc(wsize * 2 * sizeof(int) );
        if (!index || !edges) {
            printf( "Unable to allocate %d words for index or edges\n", 3 * wsize );fflush(stdout);
            MPI_Abort( MPI_COMM_WORLD, 1 );
        }
        index[0] = 2;
        for (i=1; i<wsize; i++) {
            index[i] = 2 + index[i-1];
        }
        k=0;
        for (i=0; i<wsize; i++) {
            edges[k++] = (i-1+wsize) % wsize;
            edges[k++] = (i+1) % wsize;
        }
        MPI_Graph_create( MPI_COMM_WORLD, wsize, index, edges, 0, &comm1 );
        MPI_Comm_dup( comm1, &comm2 );
        MPI_Topo_test( comm2, &topo_type );
        if (topo_type != MPI_GRAPH) {
            errs++;
            printf( "Topo type of duped graph was not graph\n" );fflush(stdout);
        }
        else {
            int nnodes, nedges;
            MPI_Graphdims_get( comm2, &nnodes, &nedges );
            if (nnodes != wsize) {
                errs++;
                printf( "Nnodes = %d, should be %d\n", nnodes, wsize );fflush(stdout);
            }
            if (nedges != 2*wsize) {
                errs++;
                printf( "Nedges = %d, should be %d\n", nedges, 2*wsize );fflush(stdout);
            }
            outindex = (int*)malloc(wsize * sizeof(int) );
            outedges = (int*)malloc(wsize * 2 * sizeof(int) );
            if (!outindex || !outedges) {
                printf( "Unable to allocate %d words for outindex or outedges\n", 3 * wsize );fflush(stdout);
                MPI_Abort( MPI_COMM_WORLD, 1 );
            }

            MPI_Graph_get( comm2, wsize, 2*wsize, outindex, outedges );
            for (i=0; i<wsize; i++) {
                if (index[i] != outindex[i]) {
                    printf( "%d = index[%d] != outindex[%d] = %d\n", index[i], i, i, outindex[i] );fflush(stdout);
                    errs++;
                }
            }
            for (i=0; i<2*wsize; i++) {
                if (edges[i] != outedges[i]) {
                    printf( "%d = edges[%d] != outedges[%d] = %d\n", edges[i], i, i, outedges[i] );fflush(stdout);
                    errs++;
                }
            }
            free( outindex );
            free( outedges );
        }
        free( index );
        free( edges );
        MPI_Comm_free( &comm2 );
        MPI_Comm_free( &comm1 );
    }

    MPI_Finalize();
    return 0;
}