Code Explanation (MPICH)
- by user243680
#include "mpi.h"
#include <stdio.h>
#include <math.h>
double f(double a)
{
return (4.0 / (1.0 + a*a));
}
void main(int argc, char *argv[])
{
int done = 0, n, myid, numprocs,i;
double PI25DT = 3.141592653589793238462643;
double mypi, pi, h, sum, x;
double startwtime, endwtime;
int namelen;
char processor_name[MPI_MAX_PROCESSOR_NAME];
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
MPI_Comm_rank(MPI_COMM_WORLD,&myid);
MPI_Get_processor_name(processor_name,&namelen);
fprintf(stderr,"Process %d on %s\n",
myid, processor_name);
fflush(stderr);
n = 0;
while (!done)
{
if (myid == 0)
{
printf("Enter the number of intervals: (0 quits) ");fflush(stdout);
scanf("%d",&n);
startwtime = MPI_Wtime();
}
MPI_Bcast(&n, 1, MPI_INT, 0, MPI_COMM_WORLD);
if (n == 0)
done = 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 is approximately %.16f, Error is %.16f\n",
pi, fabs(pi - PI25DT));
endwtime = MPI_Wtime();
printf("wall clock time = %f\n", endwtime-startwtime);
}
}
}
MPI_Finalize();
}
Can anyone explain me the above code what it does??I am in lab and my miss has asked me to explain and i dont know what it is.please help
