MPIassig2.c

#include <stdio.h>
#include <stdlib.h>
#include "mpi.h"
#define N 20

int my_reduce(int *a, int *b, int c)
{
  int i;
  for (i = 0; i < c; i++){
    b[i] = a[i] + b[i];
  }
  return 0;
}

int main(int argc, char *argv[])
{
  int i, myid, procs, val;
  MPI_Status status;
  int a[N], b[N];

  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &myid);
  MPI_Comm_size(MPI_COMM_WORLD, &procs);

  for (i = 0; i < N; i++){
    a[i] = i;
    b[i] = 0;
  }
  
  if (myid == 0){
    printf("b[%d] = %d , correct answer = %d\n", i, b[i], i*procs);
    MPI_Recv(b, N, MPI_INT, i, 0, MPI_COMM_WORLD,&status);
  }
  if (myid != 0){
    printf("b[%d] = %d , correct answer = %d\n", i, b[i], i*procs);
    MPI_Recv(b, N, MPI_INT, i, 0, MPI_COMM_WORLD,&status);
  }
  my_reduce(a, b, N);
  MPI_Send(b, N, MPI_INT, myid, 0, MPI_COMM_WORLD);
  
  MPI_Finalize();
  return 0;

}