Makes a new communicator to which topology information has been attached


#include "mpi.h"
int MPI_Graph_create ( comm_old, nnodes, index, edges, reorder, comm_graph )
MPI_Comm  comm_old;
int       nnodes;
int      *index;
int      *edges;
int       reorder;
MPI_Comm *comm_graph;

Input Parameters

comm_old input communicator without topology (handle)
nnodes number of nodes in graph (integer)
index array of integers describing node degrees (see below)
edges array of integers describing graph edges (see below)
reorder ranking may be reordered (true) or not (false) (logical)

Output Parameter

communicator with graph topology added (handle)


We ignore the reorder info currently.

Notes for Fortran

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

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


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 lastargument. Before the value is returned, the current MPI error handler iscalled. By default, this error handler aborts the MPI job. The error handlermay be changed with MPI_Errhandler_set; the predefined error handlerMPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue pastan error.

No error; MPI routine completed successfully.
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).
Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).