Date: Sat, 06 Nov 2010 01:00:34 -0700 From: perryh@pluto.rain.com To: gnrp@physik.tu-berlin.de Cc: freebsd-questions@freebsd.org Subject: Re: how to generate pi in c Message-ID: <4cd50b22.r80gL0SMmLLFy03t%perryh@pluto.rain.com> In-Reply-To: <20101105195019.4462c479@adolfputzen> References: <AANLkTikaBYi0d4dvLnc=vxuPDWQHDqrVJrz=iVkECeO=@mail.gmail.com> <20101105195019.4462c479@adolfputzen>
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Julian Fagir <gnrp@physik.tu-berlin.de> wrote:
> > Does anyone has a "generate-pi.c" source code?
...
> 1 #include <stdlib.h>
> 2 #include <string.h>
> 3 #include <stdio.h>
> 4
> 5 // Change this for a more accurate result.
> 6 long max = 100000000;
> 7 double a, b;
> 8 double pi;
> 9 long counter;
> 10 long i;
> 11
> 12 int main() {
> 13 for (i = 0; i< max; i++) {
> 14 a = drand48();
> 15 b = drand48();
> 16 if (a*a + b*b <= 1)
> 17 counter++;
> 18 }
> 19 pi = 4*counter;
> 20
> 21 printf("%e\n", pi);
> 22 return(0);
> 23 }
...
> This approximation is stupid ... Just take 'random' numbers and
> look whether they are in a circle (that's the a*a + b*b <= 1).
Not stupid, clever. Very clever. I rather doubt it resembles what
the OP had in mind, but it is a brilliant example of what can be
accomplished when one casts aside any perceived need to adopt a
conventional approach.
> The detail of this approximation heavily depends on the pseudo-rng
> you are using, as does its correctness
Perhaps it would be useful in a PRNG test suite?
> (e.g., when your 'rng' always returns 10, pi would be computed to
> be 10) ...
Bad example. If abs(drand48()) always exceeded (0.5 * sqrt(2.0)),
a*a + b*b would always exceed 1.0, thus counter would never be
incremented and pi would be reported as zero.
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