MPI求PI代码注释

[goldyellow34]

#include "stdAfx.h"
#include "mpi.h"
#include "math.h"

double f(double a){
 return(4.0/(1.0 + a * a));
}

int main(int argc, char* argv[]) {
 int flag = 0, n, myid, numprocs, i;
 double mypi, pi, h, sum, x;    
 double startwtime = 0.0, endwtime;  
 double real = 3.141592653589793236462;
 
 MPI_Init(&argc, &argv);    MPI_Comm_size(MPI_COMM_WORLD, &numprocs);   MPI_Comm_rank(MPI_COMM_WORLD, &myid);   
 n = 0;  
 while(!flag) {  
  if(myid == 0) { 
   if(n == 0) 
    n = 1000000; 
   else
    n = 0;
   startwtime = MPI_Wtime();
  }
  MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
  if(n == 0) 
   flag = 1;
  else {
   h =1.0/(double)n;
   sum = 0.0;
   for(i = myid + 1; i<= n; i += numprocs) {
    x = h * ((double)i - 0.5);
    sum += f(x);
   }
   mypi = h * sum;
   MPI_Reduce(&mypi, &pi, 1, MPI_DOUBLE,
    MPI_SUM, 0, MPI_COMM_WORLD);
   if(myid == 0) {
    printf("pi = %.16f, error = %.16f\n ", pi, fabs(pi - real));
    endwtime = MPI_Wtime();
    printf("time costs: %f\n", endwtime - startwtime);
   }
  }
 }
 MPI_Finalize();
 getchar();
 return 0;
} 

初学mpi求大虾帮忙注释下 谢谢！

[goldyellow34]

自顶，不要沉啊 求大虾指教啊

[zhuliting]

这个不是书上的例子吗？