In the example you cite below, it looks like you're mixing MPI_Gather
and MPI_Send.
MPI_Gather is a "collective" routine; it must be called by all
processes in the communicator. All processes will send a buffer/
message to the root; only the root process will receive all the
buffers/messages (note that even the root sends to itself).
MPI_Send is a point-to-point function, meaning that it is paired with
some flavor of MPI_Recv (there's a few different variants of MPI_Recv,
like MPI_Irecv, which is a non-blocking receive).
Eugene's example is a good one -- it shows point-to-point only. It
doesn't mix Gather and Recv.
On Dec 23, 2008, at 2:04 PM, Win Than Aung wrote:
Hi,
thanks for your reply. let's say i have 3 processors. I sent msg
from 1st,2nd processors and want to gather in processor 0 processor.
so i tried like following. it couldn't receive msg sent from
processor 1 and 2.
http://www.nomorepasting.com/getpaste.php?pasteid=22985
PS: is MPI_Recv is better to receive msg from multiple processors
and gather in 1 processor? or MPI_Gather is better?
thanks
winthan
On Tue, Dec 23, 2008 at 1:23 PM, Eugene Loh <eugene....@sun.com>
wrote:
Win Than Aung wrote:
MPI_Recv(....) << is it possible to receive the message sent from
other sources? I tried MPI_ANY_SOURCE in place of source but it
doesn't work out
Yes of course. Can you send a short example of what doesn't work?
The example should presumably be less than about 20 lines. Here is
an example that works:
% cat a.c
#include <stdio.h>
#include <mpi.h>
int main(int argc, char **argv) {
int np, me, sbuf = -1, rbuf = -2;
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&np);
MPI_Comm_rank(MPI_COMM_WORLD,&me);
if ( np < 2 ) MPI_Abort(MPI_COMM_WORLD,-1);
if ( me == 1 ) MPI_Send(&sbuf,1,MPI_INT,0,344,MPI_COMM_WORLD);
if ( me == 0 ) {
MPI_Recv(&rbuf,1,MPI_INT,MPI_ANY_SOURCE,
344,MPI_COMM_WORLD,MPI_STATUS_IGNORE);
if ( rbuf == sbuf ) printf("Send/Recv self passed\n");
else printf("Send/Recv self FAILED\n");
}
MPI_Finalize();
return 0;
}
% mpicc a.c
% mpirun -np 2 a.out
Send/Recv self passed
%
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Jeff Squyres
Cisco Systems
