From 2b5c0adb27d9e4d72f6d1487cc533f8671c288b9 Mon Sep 17 00:00:00 2001
From: Neil Gershenfeld <gersh@cba.mit.edu>
Date: Sat, 17 Nov 2018 12:24:58 -0500
Subject: [PATCH] wip
---
MPI/mpipi.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)
create mode 100755 MPI/mpipi.c
diff --git a/MPI/mpipi.c b/MPI/mpipi.c
new file mode 100755
index 0000000..cf4343d
--- /dev/null
+++ b/MPI/mpipi.c
@@ -0,0 +1,49 @@
+/*
+* 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();
+ }
--
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