Can you send us a small standalone test program that demonstrates the error? Rajeev On Nov 27, 2012, at 7:27 AM, Alejandro Allievi wrote:

Hi,

I'm setting up a grid topology and associated communicator using the function Setup_grid below. It works fine for process zero but throws:

Fatal error in PMPI_Comm_rank: Invalid communicator, error stack: PMPI_Comm_rank(109): MPI_Comm_rank(MPI_COMM_NULL, rank=000000000022FE4C) failed PMPI_Comm_rank(66).: Null communicator

Does MPICH2 for Win7 support topology functions???

Thanks for any help.

Alejandro

************CODE BELOW*************************** void Setup_grid(GRID_INFO_T* grid /* out */) { int old_rank; int dimensions[2]; int wrap_around[2]; int coordinates[2]; int free_coords[2];

/* Set up Global Grid Information */ MPI_Comm_size(MPI_COMM_WORLD, &(grid->p)); MPI_Comm_rank(MPI_COMM_WORLD, &old_rank);

printf("Process %d of %d inside Setup_Grid\n", old_rank, grid->p);

/* We assume p is a perfect square */ grid->q = (int) sqrt((double) grid->p); dimensions[0] = dimensions[1] = grid->q;

/* We want a circular shift in second dimension. */ /* Don't care about first */ wrap_around[0] = wrap_around[1] = 1; MPI_Cart_create(MPI_COMM_WORLD, 2, dimensions, wrap_around, 1, &(grid->comm));

MPI_Comm_rank(grid->comm, &(grid->my_rank)); MPI_Cart_coords(grid->comm, grid->my_rank, 2, coordinates); grid->my_row = coordinates[0]; grid->my_col = coordinates[1];

/* Set up row communicators */ free_coords[0] = 0; free_coords[1] = 1; MPI_Cart_sub(grid->comm, free_coords, &(grid->row_comm));

/* Set up column communicators */ free_coords[0] = 1; free_coords[1] = 0; MPI_Cart_sub(grid->comm, free_coords, &(grid->col_comm));

printf("Process %d leaving Setup_Grid\n", old_rank);

} /* Setup_grid */

-- Alejandro Allievi http://www.ace-net.ca/wiki/Alejandro_Allievi

"Tenez, mon ami, si vous y pensez bien, vous trouverez qu'en tout, notre véritable sentiment n'est pas celui dans lequel nous n'avons jamais vacillé; mais celui auquel nous sommes le plus habituellement revenus". Denis Diderot.

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