updated pi code

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;
 }

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