Approximating Π
#include <stdlib.h>
#include <stdio.h>
#include <mpi.h>
#define SEED 35791246
main(int argc, char *argv[]){
double start_time,end_time;
int niter=0;
double x,y;
int i,j,count=0,mycount,mpi_error;
double z;
double pi;
int myid,numprocs,proc,namelen;
MPI_Status status;
int master =0;
int tag = 123;
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);
if (myid == 0) {
printf("How many iterations do you want each process to do?\n ");
fflush(stdout);
scanf("%d",&niter);
}
start_time = MPI_Wtime(); /* Initialize start time */
MPI_Bcast(&niter, 1, MPI_INT, 0, MPI_COMM_WORLD);
/* Initialize random numbers */
srand(SEED+123*myid);
/*For this demonstration, just make up a different seed for each process they might not really be independent.*/
mycount=0;
for ( i=0; i<niter; i++) {
x = (double)rand()/RAND_MAX;
y = (double)rand()/RAND_MAX;
z = x*x+y*y;
if (z<=1) mycount++;
}
if (myid ==0) { /* If I am the master process gather results from others */
count=mycount;
printf("Process %d running on processor %s sending hit count= %d to master process\n",myid,processor_name,mycount );
for (proc=1; proc<numprocs; proc++) {
MPI_Recv(&mycount,1,MPI_REAL,proc,tag,MPI_COMM_WORLD,&status);
count +=mycount;
}
pi=(double)count/(niter*numprocs)*4;
printf("\n # of trials= %d , estimate of pi is %.16f \n",niter*numprocs,pi);
end_time=MPI_Wtime();
printf("Wallclock time elapsed: %.2lf seconds\n",end_time-start_time);
} else { /* for all the slave processes send results to the master */
printf("Process %d running on processor %s sending hit count= %d to master process\n",myid,processor_name,mycount );
MPI_Send(&mycount,1,MPI_REAL,master,tag,MPI_COMM_WORLD);
}
mpi_error=MPI_Finalize();
if (MPI_SUCCESS!=mpi_error)
return mpi_error;
else
return 0;
}
Two Runs
