wip

MPI/mpipi2.c

+/*
+* mpipi2.c
+* Neil Gershenfeld  2/5/11
+* use MPI to evaluate pi by summation, including overhead
+*/
+
+#include <stdio.h>
+#include <mpi.h>
+#include <sys/time.h>
+#include <stdint.h>
+
+#define NPTS 10000000000
+
+void main(int argc, char** argv) {
+   uint32_t rank,nproc;
+   uint64_t i,istart,iend,init_time,start_time,end_time;
+   struct timeval init,start,end;
+   double sum,pi,mflops;
+
+   gettimeofday(&init,NULL);
+   MPI_Init(&argc,&argv);
+   MPI_Comm_rank(MPI_COMM_WORLD,&rank);
+   MPI_Comm_size(MPI_COMM_WORLD,&nproc);
+   if (rank == 0) {
+      MPI_Barrier(MPI_COMM_WORLD);
+      gettimeofday(&start,NULL);
+      istart = 1+rank*NPTS;
+      iend = (rank+1)*NPTS;
+      sum = 0.0;
+      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);
+      init_time = init.tv_sec*1e6+init.tv_usec;
+      start_time = start.tv_sec*1e6+start.tv_usec;
+      end_time = end.tv_sec*1e6+end.tv_usec;
+      mflops = nproc*NPTS*(5.0/(end_time-start_time));
+      printf("processes = %d, NPTS = %ld, pi = %f\n",nproc,NPTS,pi);
+      printf("init = %f, time = %f, estimated MFlops = %f\n",(start_time-init_time)/1.0e6,(end_time-start_time)/1.0e6,mflops);
+      }
+   else {
+      MPI_Barrier(MPI_COMM_WORLD);
+      istart = 1+rank*NPTS;
+      iend = (rank+1)*NPTS;
+      sum = 0.0;
+      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();
+   }