From cf955b1cf3237b0841b6e10391b63b7fc75ceb00 Mon Sep 17 00:00:00 2001
From: Neil Gershenfeld <gersh@cba.mit.edu>
Date: Thu, 11 Jul 2019 21:50:37 -0400
Subject: [PATCH] wip
---
MPI/mpipi3.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)
create mode 100755 MPI/mpipi3.c
diff --git a/MPI/mpipi3.c b/MPI/mpipi3.c
new file mode 100755
index 0000000..9acbcff
--- /dev/null
+++ b/MPI/mpipi3.c
@@ -0,0 +1,59 @@
+/*
+* mpipi3.c
+* Neil Gershenfeld 7/1/19
+* use MPI to evaluate pi by summation,
+* including overhead, with multiple iterations
+*/
+
+#include <stdio.h>
+#include <mpi.h>
+#include <sys/time.h>
+#include <stdint.h>
+
+//#define NPTS 10000000000
+#define NPTS 1000000000
+#define NLOOP 10
+
+void main(int argc, char** argv) {
+ uint32_t rank,nproc;
+ uint64_t i,j,istart,iend,init_time,start_time,end_time;
+ struct timeval init,start,end;
+ double sum,pi,mflops,max;
+
+ gettimeofday(&init,NULL);
+ MPI_Init(&argc,&argv);
+ MPI_Comm_rank(MPI_COMM_WORLD,&rank);
+ MPI_Comm_size(MPI_COMM_WORLD,&nproc);
+ max = 0;
+ for (j = 0; j < NLOOP; ++j) {
+ 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\n",(start_time-init_time)/1.0e6,(end_time-start_time)/1.0e6);
+ if (mflops > max) max = mflops;
+ printf("estimated MFlops = %f, max MFlops = %f\n",mflops,max);
+ }
+ 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();
+ }
--
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