From 6fb9f35bcae368e7b67b6c3b7041999774f64918 Mon Sep 17 00:00:00 2001
From: Xin Li <lxin@kth.se>
Date: Mon, 8 Oct 2018 17:57:33 +0200
Subject: [PATCH] updated pi code
---
intro_lab/pi.c | 15 ++++++++-------
intro_lab/pi.f90 | 12 ++++++------
2 files changed, 14 insertions(+), 13 deletions(-)
diff --git a/intro_lab/pi.c b/intro_lab/pi.c
index 4307c6a..59a6b6d 100644
--- a/intro_lab/pi.c
+++ b/intro_lab/pi.c
@@ -2,6 +2,8 @@
#include <math.h>
#include <omp.h>
+#define NSTEPS 134217728
+
/*
* This program computes pi as
* \pi = 4 arctan(1)
@@ -9,24 +11,23 @@
*/
int main(int argc, char** argv)
{
- unsigned long nsteps = 100000000;
- double dx = 1.0 / nsteps;
-
+ long i;
+ double dx = 1.0 / NSTEPS;
double pi = 0.0;
+
double start_time = omp_get_wtime();
- unsigned long i;
- for (i = 0; i < nsteps; i++)
+ for (i = 0; i < NSTEPS; i++)
{
double x = (i + 0.5) * dx;
pi += 1.0 / (1.0 + x * x);
}
- pi *= 4.0 * dx;
+ pi *= 4.0 * dx;
double run_time = omp_get_wtime() - start_time;
double ref_pi = 4.0 * atan(1.0);
printf("pi with %ld steps is %.10f in %.6f seconds (error=%e)\n",
- nsteps, pi, run_time, fabs(ref_pi - pi));
+ NSTEPS, pi, run_time, fabs(ref_pi - pi));
return 0;
}
diff --git a/intro_lab/pi.f90 b/intro_lab/pi.f90
index c045292..127a5fe 100644
--- a/intro_lab/pi.f90
+++ b/intro_lab/pi.f90
@@ -8,25 +8,25 @@ use omp_lib
implicit none
-integer(kind=8) :: nsteps, i
+integer(kind=8), parameter :: NSTEPS = 134217728
+
+integer(kind=8) :: i
real(kind=8) :: dx, x, pi, ref_pi
real(kind=8) start_time, run_time
-nsteps = 100000000
-dx = 1.0D0 / nsteps
+dx = 1.0D0 / NSTEPS
pi = 0.0D0
start_time = OMP_GET_WTIME()
-do i = 1, nsteps
+do i = 1, NSTEPS
x = (i - 0.5D0) * dx
pi = pi + 1.0D0 / (1.0D0 + x * x)
enddo
pi = pi * 4.0D0 * dx
-
run_time = OMP_GET_WTIME() - start_time
ref_pi = 4.0D0 * atan(1.0D0)
-print '("pi with ", i0, " steps is ", f16.10, " in ", f12.6, " seconds (error=", e12.6, ")")', nsteps, pi, run_time, abs(ref_pi - pi)
+print '("pi with ", i0, " steps is ", f16.10, " in ", f12.6, " seconds (error=", e12.6, ")")', NSTEPS, pi, run_time, abs(ref_pi - pi)
end program
--
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