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Re: parabolic trough edge's length
From: mrdovey@iedu.com (Morris Dovey)
With the given values for f and dr, it gets results correct to ten
significant digits, but on my machine takes about ten minutes to do
it How long does it take on your computer?
I suspect that the long runtime is a result of (re)interpreting the BASIC source code 100,000 times, rather than a slow processor.
I disposed of my BASIC interpreter not too long after Nick stopped posting code, so I can't run your code as-is - but I transliterated to C
#include <stdio.h>
#include <math.h>
int main(void)
{ double f = 1; /* focal length */
double dr = f / 100000; /* step size */
double d2 = dr / 2;
double k = 4 * f * f;
double t = 0;
double r = d2;
double r2,q,d,a;
do
{ r2 = r * r;
q = r * (k - r2) * sqrt(k + r2);
t = t + q;
r = r + dr;
} while (t > 0);
r = r - d2 - dr * t / q;
d = r * r / (4 * f);
a = atan(r / (d - f)) * 45 / atan(1);
printf("Focal length: %G\n",f);
printf("Depth of dish: %G\n",d);
printf("Radius of rim: %G\n",r);
printf("Angular radius of rim, seen from focus %G degrees",a);
return 0;
}
then compiled and linked. When I ran the executable I got
C:\usr\mrd\c> dow
Focal length: 1
Depth of dish: 1.84781
Radius of rim: 2.71868
Angular radius of rim, seen from focus 72.6801 degrees
C:\usr\mrd\c>
in just under 5 seconds.
Not quite enough time to go for coffee :(
--
Morris Dovey
