[OMPI users] MPI_Alltoall with Vector Datatype

[Spenser Gilliland]

Hi,

I've recently started working with MPI and I noticed that when a
Alltoall is utilized with a vector datatype, the call only uses the
extent to determine the location for the back to back transactions.
This makes using the vector type with collective communicators
difficult.

For Example:
Using the code at the bottom.  I think I should get

 0  1  8  9
 4  5 12 13
 2  3 10 11
 6  7 14 15

However, the result is

 0  1  2  3
 4  5  8  9
 6  7 10 11
 x  x 14 15

Is this the way it is supposed to be?

FYI: This is version 1.6.2 in Rocks 6

Thanks,
Spenser

float A[4][4];
int wsize, wrank;
MPI_Comm_size(MPI_COMM_WORLD, &wsize); // Assume 2
MPI_Comm_rank(MPI_COMM_WORLD, &wrank);
MPI_Type_vector(4/wsize, 4/wsize, 4, MPI_FLOAT, &mpi_all_t);
MPI_Type_commit(&mpi_all_t);

for(int i = 0; i < 4; i++) for (j = 0; j < 4; j++) {
   A[i][j] = i*4+j;
}

MPI_Alltoall(A[rank*4/wsize*4], 1, mpi_all_t,
                     A[rank*4/wsize*4], 1, mpi_all_t,
                     MPI_COMM_WORLD);

for(int i = 0; i < 4; i++) {
   for (j = 0; j < 4; j++) {
      printf("%6.2g")
   }
   printf("\n");
}

-- 
Spenser Gilliland
Computer Engineer
Doctoral Candidate