Hello World Program

The "Hello World" program was my first test of the parallel processor. The way it works is this. A string is send around to each process and each process appends a string to it and send it on. Process 0 starts it off, and then sends it on to process 1. Process 1 sends it to process 2, etc.
This is written as one program that gets copied to each processor. This is the listing of the program:

#include <mpi.h>
#include <stdio.h>

main(int argc, char *argv[])
{
char message[1024];
int rank,numnodes;
char node[2];
MPI_Status stat;

MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
node[0] = rank + '0';
node[1] = '\0';
MPI_Comm_size(MPI_COMM_WORLD, &numnodes);
if (rank == 0)
    {
      printf("\n\nRunning %d processes.\n\n",numnodes);
      strcpy(message,"Hello World from process 0.");
      if (numnodes != 0)
        {
          MPI_Send(message,strlen(message),MPI_CHAR,1,11,MPI_COMM_WORLD);
          MPI_Recv(message,1024,MPI_CHAR,numnodes-1,11,MPI_COMM_WORLD,&stat);
        }
      printf("\n\n%s\n\n",message);
    }
else
    {
      MPI_Recv(message,1024,MPI_CHAR,rank-1,11,MPI_COMM_WORLD,&stat);
      strcat(message,"\nHello World from process ");
      strcat(message,node);
      strcat(message,".");
      if (rank < numnodes-1)
        MPI_Send(message,strlen(message),MPI_CHAR,rank+1,11,MPI_COMM_WORLD);
      else
        MPI_Send(message,strlen(message),MPI_CHAR,0,11,MPI_COMM_WORLD);
    }
MPI_Finalize();
}

Compile the program with "hcc:

hcc hello.c -lmpi -o hello and run the program with the "mpirun" program

mpirun -w N hello -s h the output is like this:

Hello World from process 0.
Hello World from process 1.
Hello World from process 2.
Hello World from process 3.

For more information on the mpirun and hcc commands try the man pages included with Lam-MPI.

Written by: David Randall
randaldt@acad.etown.edu
http://www.etown.edu/~randaldt