Hi
I think the problem is the way you build the columns [][] array and send..
When offset starts at 0 -> you call MPI_Send (& columns, count, ...)
But when offset is not 0 you want to MPI_Send (& (columns+offset), count,
... )
That would explain why you are receiving crap -> always sending columns [0]
... columns [count - 1] and they're not initialized.
Regards,
Lee
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;
On 7/7/06, Raúl González <revenant81_at_[hidden]> wrote:
>
> 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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