From Debian Clusters

Quite a few of the tutorials call for a simple MPI program, so here's one below, written in C. This is borrowed from the Bootable Cluster CD project, which I used to contribute to.

Creating the Program

Open up your favorite text editor and type the following, then save it as helloworld.c. This program uses a common paradigm where one process acts as a "server process" and the rest as "client processes". The client processes will send a message to the server process, which will then print them out along with a message of its own.

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

int main(int argc, char ** argv) {

	int size,rank;
	int length;
	char name[80];
	MPI_Status status;
	int i;

	MPI_Init(&argc, &argv);
	// note that argc and argv are passed by address

	MPI_Comm_rank(MPI_COMM_WORLD,&rank);
	MPI_Comm_size(MPI_COMM_WORLD,&size);
	MPI_Get_processor_name(name,&length);

	if (rank==0) {
     	// server commands
		printf("Hello MPI from the server process!\n");
		for (i=1;i<size;i++) {
			MPI_Recv(name,80,MPI_CHAR,i,999,MPI_COMM_WORLD,&status);
			printf("Hello MPI!\n");
			printf(" mesg from %d of %d on %s\n",i,size,name);
		}
	} else {
		// client commands
		MPI_Send(name,80,MPI_CHAR,0,999,MPI_COMM_WORLD);
	}

	MPI_Finalize(); 
}

Compiling

To compile an MPI program written in C, run

mpicc -o hello.out helloworld.c

• -o hello.out is an optional command that specifies the output file name, otherwise the file is named with the default a.out

Note: mpicxx will compile C++ programs with MPI, mpif77 will compile Fortran 77 MPI programs, and mpif90 will compile Fortran 90 MPI programs.