George,
> Do you mind posting your working example here on the mailing list?
> This might help future users understanding how to correctly use the
> MPI datatype.
No problem. I wrote up this simplified example so others can learn to
use the functionality. This is a matrix transpose operation using MPI
vector derived types and collective communication. (Terms added to aid
search engines)
The result of running this program with a two node cluster is
Matrix =
0: 0 1 2 3 4 5 6 7
0: 8 9 10 11 12 13 14 15
0: 16 17 18 19 20 21 22 23
0: 24 25 26 27 28 29 30 31
1: 32 33 34 35 36 37 38 39
1: 40 41 42 43 44 45 46 47
1: 48 49 50 51 52 53 54 55
1: 56 57 58 59 60 61 62 63
Matrix =
0: 0 8 16 24 4 12 20 28
0: 1 9 17 25 5 13 21 29
0: 2 10 18 26 6 14 22 30
0: 3 11 19 27 7 15 23 31
1: 32 40 48 56 36 44 52 60
1: 33 41 49 57 37 45 53 61
1: 34 42 50 58 38 46 54 62
1: 35 43 51 59 39 47 55 63
Matrix =
0: 0 8 16 24 32 40 48 56
0: 1 9 17 25 33 41 49 57
0: 2 10 18 26 34 42 50 58
0: 3 11 19 27 35 43 51 59
1: 4 12 20 28 36 44 52 60
1: 5 13 21 29 37 45 53 61
1: 6 14 22 30 38 46 54 62
1: 7 15 23 31 39 47 55 63
/* file: transpose.c
*
* Description: Transpose operation using MPI derived datatypes with
* MPI collective communications.
*
* Author: Spenser Gilliland <spen...@gillilanding.com>
*/
#include <mpi.h>
#include <stdio.h>
#include <unistd.h>
#define N (8)
float matrix[N][N];
void print_matrix(int wrank, int wrows) {
int i , j;
MPI_Barrier(MPI_COMM_WORLD);
if(wrank == 0) printf("Matrix = \n");
MPI_Barrier(MPI_COMM_WORLD);
for(i = 0; i < N; i++) {
if(i >= wrank*wrows && i < (wrank+1)*wrows) {
printf("%2d:", wrank);
for(j = 0; j < N; j++) {
printf("%6.2g", matrix[i][j]);
}
printf("\n");
}
usleep(1);
MPI_Barrier(MPI_COMM_WORLD);
}
}
int main(int argc, char *argv[]) {
int wsize, wrank, wrows;
int i, j, k;
int row, col;
float temp;
MPI_Datatype mpi_all_unaligned_t, mpi_all_t;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &wsize);
MPI_Comm_rank(MPI_COMM_WORLD, &wrank);
wrows = N / wsize;
MPI_Type_vector(N, wrows, N, MPI_FLOAT, &mpi_all_unaligned_t);
MPI_Type_create_resized(mpi_all_unaligned_t, 0,
wrows*sizeof(float), &mpi_all_t);
MPI_Type_free(&mpi_all_unaligned_t);
MPI_Type_commit(&mpi_all_t);
for(i = 0; i < N; i++) {
/* Initialize data on the rows of the matrix owned by this rank */
if (i >= wrank*wrows && i < (wrank+1)*wrows) {
for(j = 0; j < N; j++) {
matrix[i][j] = i*N + j;
}
}
}
print_matrix(wrank, wrows);
/* Local Transpose */
row = wrank*wrows;
for(k = 0; k < wsize; k++) {
col = k*wrows;
for( i = 0; i < wrows; i++) {
for(j =i+1; j < wrows; j++) {
temp = matrix[row+i][col + j];
matrix[row + i][col + j] = matrix[row + j][col + i];
matrix[row + j][col + i] = temp;
}
}
}
print_matrix(wrank, wrows);
/* Global Transpose */
MPI_Alltoall(matrix[wrank*wrows], 1, mpi_all_t,
matrix[wrank*wrows], 1, mpi_all_t,
MPI_COMM_WORLD);
print_matrix(wrank, wrows);
MPI_Finalize();
return 0;
}
Thanks,
Spenser
