#include <stdio.h>
#include <time.h>
#include <math.h>
#include <mpi.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/times.h>
clock_t u_clock()
 { struct tms t;
   return times(&t); }
int main(int argc, char* argv[])
{ int np, nr;
  clock_t t1, t2;
  long long int i, nn, ns, n=10000000000;
  double pi=0.0, x, use, pis[50];
  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &np);
  MPI_Comm_rank(MPI_COMM_WORLD, &nr);
  nn = n/np;
  ns = nr*nn;
  t1 = u_clock();
#pragma omp parallel for private(i,x) reduction(+:pi)
  for (i=ns+1; i<=ns+nn; i++)
    { x  = i;
      pi = pi + 6.0/(x*x); }
  MPI_Gather(&pi,1,MPI_REAL8,pis,1,MPI_REAL8,
             0,MPI_COMM_WORLD);
  if(nr == 0)
    { pi = 0.0;
      for (i=0; i<np; i++)
        { pi += pis[i]; }
      t2 = u_clock(); 
      use = (double)(t2 - t1)/100.0;
      pi = sqrt(pi);
      printf("np=%d, n=%ld, pi=%f\n",np,n,pi);
      printf(" use time=%f  sec\n",use);
    }
  MPI_Finalize();
  return 0; }