gsizes[0] = m; /* no. of rows in global array */ gsizes[1] = n; /* no. of columns in global array*/ psizes[0] = 2; /* no. of processes in vertical dimension of process grid */ psizes[1] = 3; /* no. of processes in horizontal dimension of process grid */ lsizes[0] = m/psizes[0]; /* no. of rows in local array */ lsizes[1] = n/psizes[1]; /* no. of columns in local array */ dims[0] = 2; dims[1] = 3; periods[0] = periods[1] = 1; MPI_Cart_create(MPI_COMM_WORLD, 2, dims, periods, 0, &comm); MPI_Comm_rank(comm, &rank); MPI_Cart_coords(comm, rank, 2, coords); /* global indices of the first element of the local array */ start_indices[0] = coords[0] * lsizes[0]; start_indices[1] = coords[1] * lsizes[1]; MPI_Type_create_subarray(2, gsizes, lsizes, start_indices, MPI_ORDER_C, MPI_FLOAT, &filetype); MPI_Type_commit(&filetype); MPI_File_open(comm, "/pfs/datafile", MPI_MODE_CREATE | MPI_MODE_WRONLY, MPI_INFO_NULL, &fh); MPI_File_set_view(fh, 0, MPI_FLOAT, filetype, "native", MPI_INFO_NULL); local_array_size = lsizes[0] * lsizes[1]; MPI_File_write_all(fh, local_array, local_array_size, MPI_FLOAT, &status); MPI_File_close(&fh);