wip

MPI/mpipi.c

+/*
+* mpipi.c
+* Neil Gershenfeld  2/5/11
+* use MPI to evaluate pi by summation
+*/
+
+#include <stdio.h>
+#include <mpi.h>
+#include <sys/time.h>
+
+#define NPTS 100000000
+#define NLOOP 10
+
+void main(int argc, char** argv) {
+   int rank,nproc,i,istart,iend,loop,N;
+   unsigned long int start_time,end_time;
+   struct timeval start,end;
+   double sum,pi,mflops;
+
+   MPI_Init(&argc, &argv);
+   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+   MPI_Comm_size(MPI_COMM_WORLD, &nproc);
+   if (rank == 0) {
+      gettimeofday(&start, NULL);
+      istart = 1 + NPTS*((rank+0.0)/nproc);
+      iend = NPTS*((rank+1.0)/nproc);
+      sum = 0.0;
+      for (loop = 0; loop < NLOOP; ++loop)
+         for (i = istart; i <= iend; ++i)
+            sum += 0.5/((i-0.75)*(i-0.25));
+      MPI_Reduce(&sum,&pi,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
+      gettimeofday(&end, NULL);
+      start_time = start.tv_sec * 1e6 + start.tv_usec;
+      end_time = end.tv_sec * 1e6 + end.tv_usec;
+      mflops = NLOOP*(NPTS*(5.0/(end_time-start_time)));
+      printf("processes = %d, NPTS = %d, NLOOP = %d, pi = %f\n",nproc,NPTS,NLOOP,pi/NLOOP);
+      printf("time = %f, estimated MFlops = %f\n",(end_time-start_time)/1.0e6,mflops);
+      }
+   else {
+      istart = 1 + NPTS*((rank+0.0)/nproc);
+      iend = NPTS*((rank+1.0)/nproc);
+      sum = 0.0;
+      for (loop = 0; loop < NLOOP; ++loop)
+         for (i = istart; i <= iend; ++i)
+            sum += 0.5/((i-0.75)*(i-0.25));
+      MPI_Reduce(&sum,&pi,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
+      }
+   MPI_Finalize();
+   }