#include "mpi.h"int main( int argc, char *argv[] ){    int          gsizes[2], distribs[2], dargs[2], psizes[2], rank, size, m, n;    int          lsizes[2], dims[2], periods[2], coords[2], start_indices[2];    int          memsizes[2];    MPI_Datatype filetype, memtype;    MPI_Comm     comm;    int          local_array_size, num_local_rows, num_local_cols;    int          row_procs, col_procs, row_rank, col_rank;    MPI_File     fh;     float        *local_array;     MPI_Status   status;    MPI_Init( &argc, &argv );    /* ... */    /* This code is particular to a 2 x 3 process decomposition */    MPI_Comm_size( MPI_COMM_WORLD, &size );    if (size != 6) {	printf( "Communicator size must be 6\n" );	MPI_Abort( MPI_COMM_WORLD, 1 );    }    /* See comments on block distribution */    row_procs = 2;    col_procs = 3;    num_local_rows = (m + row_procs - 1) / row_procs;    /* adjust for last row */    if (row_rank == row_procs-1) 	num_local_rows = m - (row_procs-1) * num_local_rows;    num_local_cols = (n + col_procs - 1) / col_procs;    /* adjust for last column */    if (col_rank == col_procs-1) 	num_local_cols = n - (col_procs-1) * num_local_cols;    local_array = (float *)malloc( num_local_rows * num_local_cols * sizeof(float) );    /* ... set elements of local_array ... */    gsizes[0] = m;    gsizes[1] = n;        /* no. of rows and columns in global array*/    psizes[0] = 2;    psizes[1] = 3;        /* no. of processes in vertical and horizontal dimensions        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(MPI_COMM_WORLD, "/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);    /* create a derived datatype that describes the layout of the local        array in the memory buffer that includes the ghost area. This is        another subarray datatype! */    memsizes[0] = lsizes[0] + 8; /* no. of rows in allocated array */    memsizes[1] = lsizes[1] + 8; /* no. of columns in allocated array */    start_indices[0] = start_indices[1] = 4;     /* indices of the first element of the local array in the       allocated array */    MPI_Type_create_subarray(2, memsizes, lsizes, start_indices, 			     MPI_ORDER_C, MPI_FLOAT, &memtype);    MPI_Type_commit(&memtype);    MPI_File_write_all(fh, local_array, 1, memtype, &status);    MPI_File_close(&fh);    /* ... */    MPI_Finalize();    return 0;}