I'm trying to do some simple programs with MPI and C to get familiarized with them.
I was trying to multiply a couple of arrays (A and B), sending part of the arrays to a couple of tasks (half of the rows of A and half of the columns of B to one task and the rest to the other) but for some reason I get some weird values for the columns of B I sent to the second task.
I'm using MPI_Send and MPI_Recv and all seems to be alright. This is the relevant code from the master node:
printf("\nSending %d rows from A and %d colums from B to node %d\n", rows, rows, i);
printf("Sending the offset (%d) to task %d\n", offset, i);
MPI_Send(&offset, 1, MPI_INT, i, 0, MPI_COMM_WORLD);
printf("Sending the number of rows (%d) to task %d\n", rows, i);
MPI_Send(&rows, 1, MPI_INT, i, 0, MPI_COMM_WORLD);
// We send the corresponding rows of A
count = rows * elements;
printf("Sending the rows from A to task %d\n", i);
MPI_Send(&A[offset][0], count, MPI_INT, i, 0, MPI_COMM_WORLD);
// and columns from B
printf("Sending the columns from B to task %d\n", i);
int columns[elements][rows];
for (j = 0; j < elements; j++)
for (k = offset; k < offset + rows; k++)
columns[j][k] = B[j][k];
MPI_Send(&columns, count, MPI_INT, i, 0, MPI_COMM_WORLD);
// For the next task the data to be sent will start where this one ended
offset = offset + rows;
When I print the content of columns here, before seding it, all seems to be ok, so I guess I get the fake values because I don't use MPI_Send or Recive as they are supoused to be used, or because of something I did wrong when I recived it. This is the code for the worker nodes:
// Recive the info
MPI_Recv(&offset, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
printf ("Task %d recived %d as offset\n", id, offset);
MPI_Recv(&rows, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
printf ("Task %d recived %d as rows to be sent\n", id, rows);
printf ("Task %d got %d as number of elements per row with broadcasting\n", id, elements);
count = rows * elements;
MPI_Recv(&A, count, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
printf ("Task %d recived %d elements from matrix A:\n", id, count);
for (i = 0; i < rows; i++) {
for (j = 0; j < elements; j++)
printf("%d ", A[i][j]);
printf("\n");
}
int columns[elements][rows];
MPI_Recv(&columns, count, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
printf ("Task %d recived %d elements from matrix B:\n", id, count);
I am not really a regular C programmer, so there could be something really wrong with my code, but I don't understand why I am getting crap on my MPI_Recv calls.
This is an example of the execution of the program:
A:
62 27 88 57
21 94 60 17
91 28 14 3
81 50 53 71
B:
34 34 76 43
13 0 17 57
96 36 23 58
26 87 17 15
The first worker node got two rows from A:
62 27 88 57
21 94 60 17
and two columns from B:
34 34
13 0
96 36
26 87
And the second one got the other two rows from A:
91 28 14 3
81 50 53 71
and two columns from B, but with a couple of fake values wich are the ones that ruin it all:
134516401 134519392
76 43
17 57
23 58
If someone could throw some light upon this, I'd be grateful.
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