--- /dev/null
+/* A first simple SPMD example program using MPI */
+
+/* The program consists of on receiver process and N-1 sender */
+/* processes. The sender processes send a message consisting */
+/* of their process identifier (id) and the total number of */
+/* processes (ntasks) to the receiver. The receiver process */
+/* prints out the values it receives in the messeges from the */
+/* senders. */
+
+/* Compile the program with 'mpicc first.c -o first' */
+/* To run the program, using four of the computers specified in */
+/* your hostfile, do 'mpirun -machinefile hostfile -np 4 first */
+
+#include <stdio.h>
+#include <mpi.h>
+
+main(int argc, char *argv[]) {
+ const int tag = 42; /* Message tag */
+ int id, ntasks, source_id, dest_id, err, i;
+ MPI_Status status;
+ int msg[2]; /* Message array */
+
+ err = MPI_Init(&argc, &argv); /* Initialize MPI */
+ if (err != MPI_SUCCESS) {
+ printf("MPI initialization failed!\n");
+ exit(1);
+ }
+ err = MPI_Comm_size(MPI_COMM_WORLD, &ntasks); /* Get nr of tasks */
+ err = MPI_Comm_rank(MPI_COMM_WORLD, &id); /* Get id of this process */
+ if (ntasks < 2) {
+ printf("You have to use at least 2 processors to run this program\n");
+ MPI_Finalize(); /* Quit if there is only one processor */
+ exit(0);
+ }
+
+ if (id == 0) { /* Process 0 (the receiver) does this */
+ for (i=1; i<ntasks; i++) {
+ err = MPI_Recv(msg, 2, MPI_INT, MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, \
+ &status); /* Receive a message */
+ source_id = status.MPI_SOURCE; /* Get id of sender */
+ printf("Received message %d %d from process %d\n", msg[0], msg[1], \
+ source_id);
+ }
+ }
+ else { /* Processes 1 to N-1 (the senders) do this */
+ msg[0] = id; /* Put own identifier in the message */
+ msg[1] = ntasks; /* and total number of processes */
+ dest_id = 0; /* Destination address */
+ sleep(3);
+ err = MPI_Send(msg, 2, MPI_INT, dest_id, tag, MPI_COMM_WORLD);
+ }
+
+ err = MPI_Finalize(); /* Terminate MPI */
+ if (id==0) printf("Ready\n");
+ return 0;
+}
+
