Cartesian Convenience Function: MPI_DIMS_CREATE

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Cartesian Convenience Function: MPI_DIMS_CREATE

For Cartesian topologies, the function MPI_DIMS_CREATE helps the user select a balanced distribution of processes per coordinate direction, depending on the number of processes in the group to be balanced and optional constraints that can be specified by the user. One possible use of this function is to partition all the processes (the size of MPI_COMM_WORLD's group) into an n -dimensional topology.

 MPI_DIMS_CREATE(nnodes, ndims, dims)

   IN       nnodes            number of nodes in a grid
   IN       ndims             number of cartesian dimensions
   INOUT    dims              integer array of size ndims 
                              specifying the number of nodes 
                              in each dimension.
MPI_Dims_create(int nnodes, int ndims, int *dims)


The entries in the array dims are set to describe a Cartesian grid with ndims dimensions and a total of nnodes nodes. The dimensions are set to be as close to each other as possible, using an appropriate divisibility algorithm. The caller may further constrain the operation of this routine by specifying elements of array dims. If dims[i] is set to a positive number, the routine will not modify the number of nodes in dimension i; only those entries where dims[i] = 0 are modified by the call.

Negative input values of dims[i] are erroneous. An error will occur if nnodes is not a multiple of .

For dims[i] set by the call, dims[i] will be ordered in monotonically decreasing order. Array dims is suitable for use as input to routine MPI_CART_CREATE. MPI_DIMS_CREATE is local. Several sample calls are shown in Example gif.

Jack Dongarra
Fri Sep 1 06:16:55 EDT 1995