Hi,
I have built openmpi-1.9a1r27380 with Java support and try some small
programs. When I try to Send/Recv the columns of a matrix, I don't get
the expected results. I used "offset = 0" instead of "offset = i"
in MPI.COMM_WORLD.Send for the following output, so that all processes
should have received the first column.
tyr java 115 mpijavac ColumnSendRecvMain.java
tyr java 116 mpiexec -np 7 java ColumnSendRecvMain
matrix:
1.00 2.00 3.00 4.00 5.00 6.00
7.00 8.00 9.00 10.00 11.00 12.00
13.00 14.00 15.00 16.00 17.00 18.00
19.00 20.00 21.00 22.00 23.00 24.00
Column of process 5
Column of process 1
0.00 3.00 7.00 0.00
0.00 3.00 7.00 0.00
...
I use the following program.
import mpi.*;
public class ColumnSendRecvMain
{
static final int P = 4; /* # of rows */
static final int Q = 6; /* # of columns */
static final int NUM_ELEM_PER_LINE = 6; /* to print a vector */
public static void main (String args[]) throws MPIException
{
int ntasks, /* number of parallel tasks */
mytid, /* my task id */
i, j, /* loop variables */
tmp; /* temporary value */
double matrix[][],
column[];
Datatype column_t; /* strided vector */
MPI.Init (args);
matrix = new double[P][Q];
column = new double[P];
mytid = MPI.COMM_WORLD.Rank ();
ntasks = MPI.COMM_WORLD.Size ();
/* check that we have the correct number of processes in our
* universe
*/
if (mytid == 0)
{
if (ntasks != (Q + 1))
{
System.err.println ("\n\nI need exactly " + (Q + 1) +
" processes.\n\n" +
"Usage:\n" +
" mpiexec -np " + (Q + 1) +
" java <program name>\n");
}
}
if (ntasks != (Q + 1))
{
MPI.Finalize ();
System.exit (0);
}
/* Build the new type for a strided vector. */
column_t = Datatype.Vector (P, 1, Q, MPI.DOUBLE);
column_t.Commit ();
if (mytid == 0)
{
tmp = 1;
for (i = 0; i < P; ++i) /* initialize matrix */
{
for (j = 0; j < Q; ++j)
{
matrix[i][j] = tmp++;
}
}
System.out.println ("\nmatrix:\n"); /* print matrix */
for (i = 0; i < P; ++i)
{
for (j = 0; j < Q; ++j)
{
System.out.printf ("%10.2f", matrix[i][j]);
}
System.out.println ();
}
System.out.println ();
}
if (mytid == 0)
{
/* send one column to each process */
for (i = 0; i < Q; ++i)
{
MPI.COMM_WORLD.Send (matrix, i, 1, column_t, i + 1, 0);
}
}
else
{
MPI.COMM_WORLD.Recv (column, 0, P, MPI.DOUBLE, 0, 0);
/* Each process prints its column. The output will probably
* intermingle on the screen so that you must use
* "-output-filename" in Open MPI.
*/
System.out.println ("\nColumn of process " + mytid + "\n");
for (i = 0; i < P; ++i)
{
if (((i + 1) % NUM_ELEM_PER_LINE) == 0)
{
System.out.printf ("%10.2f\n", column[i]);
}
else
{
System.out.printf ("%10.2f", column[i]);
}
}
System.out.println ();
}
column_t.finalize ();
MPI.Finalize();
}
}
In my opinion Datatype.Vector doesn't work as expected. mpiJava doesn't
support something similar to MPI_Type_create_resized so how can I use
column_t in a scatter operation? Will scatter automatically start with
the next element and not with the element following the extent of
column_t? Is the wrong output of my program related to a bug in the
mpiJava operation, so that I must wait for a fix or do I make a mistake
in my program? Thank you very much for any help in advance.
Kind regards
Siegmar
