Level-3 Access
Similar to level 2, except that each process uses collective I/O functions
MPI_Type_create_subarray(..., &subarray, ...);
MPI_Type_commit(&subarray);
MPI_File_open(MPI_COMM_WORLD, file, ..., &fh);
MPI_File_set_view(fh, ..., subarray, ...);
MPI_File_read_all(fh, A, ...);