MPI and OpenMP Example

hybrid.c

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

int main(int argc, char *argv[])
{
    int numprocs, rank, namelen;
    char processor_name[MPI_MAX_PROCESSOR_NAME];
    int iam = 0, np = 1;

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Get_processor_name(processor_name, &namelen);

    #pragma omp parallel default(shared) private(iam, np)
    {
        np = omp_get_num_threads();
        iam = omp_get_thread_num();
        printf("Hybrid: Hello from thread %d out of %d from process %d out of %d on %s\n",
                iam, np, rank, numprocs, processor_name);
    }

    MPI_Finalize();

    return 0;
}

Makefile

BINS:= mpi greetings omp hybrid

all: $(BINS)

mpi: mpi-hello.c
	mpicc -o mpi mpi-hello.c

greetings: mpi-greetings.c
	mpicc -o greetings mpi-greetings.c

omp: omp-hello.c
	gcc -fopenmp -o omp omp-hello.c

hybrid: hybrid.c
	mpicc -openmp -lgomp -o hybrid hybrid.c

test: $(BINS)
	@echo "Test MPI..."
	@mpirun -np 4 ./mpi
	@mpirun -np 4 ./greetings
	@echo "Test OpenMP..."
	@./omp
	@echo "Test Hybrid..."
	@mpirun -np 4 ./hybrid

clean:
	@rm -f $(BINS)

mpi-greetings.c

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

#define MSG_LEN 128
#define MSG_TAG 99

int main(int argc, char *argv[])
{
    int world_rank = 0, world_size = 0, name_len = 0, i = 0;
    char processor_name[MPI_MAX_PROCESSOR_NAME] = { 0x0 };
    char msg[MSG_LEN] = { 0x0 };
    MPI_Status status;

    /* MPI_Init(NULL, NULL); */
    MPI_Init(&argc, &argv); /* 程序初始化 */
    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank); /* 得到当前进程号 */
    MPI_Comm_size(MPI_COMM_WORLD, &world_size); /* 得到总的进程数 */
    MPI_Get_processor_name(processor_name, &name_len); /* 得到机器名 */

    if (world_rank != 0) {
        sprintf(msg, "MPI: Greetings from %s, rank %d out of %d", processor_name, world_rank, world_size);
        MPI_Send(msg, strlen(msg) + 1, MPI_CHAR, 0, MSG_TAG, MPI_COMM_WORLD);
    } else {
        printf("MPI: Greetings from %s, rank %d out of %d\n", processor_name, world_rank, world_size);
        for(i = 1; i < world_size; i++) {
            MPI_Recv(msg, MSG_LEN, MPI_CHAR, i, MSG_TAG, MPI_COMM_WORLD, &status);
            printf("%s\n", msg);
        }
    }

    MPI_Finalize(); /* 结束 */

    return 0;
}

mpi-hello.c

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

int main(int argc, char *argv[])
{
    int world_rank, world_size;
    int name_len;
    char processor_name[MPI_MAX_PROCESSOR_NAME];

    /* MPI_Init(NULL, NULL); */
    MPI_Init(&argc, &argv); /* 程序初始化 */
    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank); /* 得到当前进程号 */
    MPI_Comm_size(MPI_COMM_WORLD, &world_size); /* 得到总的进程数 */
    MPI_Get_processor_name(processor_name, &name_len); /* 得到机器名 */

    printf("MPI: Hello world from %s, rank %d out of %d\n", processor_name, world_rank, world_size);

    MPI_Finalize(); /* 结束 */

    return 0;
}

omp-hello.c

#include <omp.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
    int nthreads, tid;

/* Fork a team of threads giving them their own copies of variables */
#pragma omp parallel private(nthreads, tid)
    {
        /* Obtain thread number */
        tid = omp_get_thread_num();
        printf("OpenMP: Hello World from thread = %d\n", tid);

        /* Only master thread does this */
        if (tid == 0)
        {
            nthreads = omp_get_num_threads();
            printf("OpenMP: Number of threads = %d\n", nthreads);
        }
    } /* All threads join master thread and disband */

    return 0;
}

in the Makefile there is a typo:
at line 15 you should add "-fopenmp". To be specific line 15 of Makefile should be
mpicc -openmp -lgomp -fopenmp -o hybrid hybrid.c
otherwise hyprid.c is not compiled.