Exemple : Pi

Contenu du fichier

#include "mpi.h" 
#include <stdio.h> 
#include <math.h> 
int main( int argc, char *argv[] ) 
{ 
   int n, myid, numprocs, i; 
   double PI25DT = 3.141592653589793238462643; 
   double mypi, pi, h, sum, x; 
   MPI_Init(&argc,&argv); 
   MPI_Comm_size(MPI_COMM_WORLD,&numprocs); 
   MPI_Comm_rank(MPI_COMM_WORLD,&myid); 
   while (1) { 
      if (myid == 0) { 
          printf("Enter the number of intervals: (0 quits) "); 
          scanf("%d",&n); 
      } 
      MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD); 
      if (n == 0) 
          break; 
      else { 
         h   = 1.0 / (double) n; 
         sum = 0.0; 
         for (i = myid + 1; i <= n; i += numprocs) { 
             x = h * ((double)i - 0.5); 
             sum += (4.0 / (1.0 + x*x)); 
         } 
         mypi = h * sum; 
         MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE, MPI_SUM, 0, 
                    MPI_COMM_WORLD); 
         if (myid == 0)  
             printf("pi is approximately %.16f, Error is %.16f\n", 
                    pi, fabs(pi - PI25DT)); 
      } 
   } 
   MPI_Finalize(); 
   return 0; 
}