Javascript: gamma approximation Post: 302876504

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Top Forums Programming Javascript: gamma approximation Post 302876504 by figaro on Monday 25th of November 2013 06:10:57 AM

11-25-2013

Registered User

Javascript: gamma approximation

Here is some javascript code that implements the Lanczos approximation to the gamma function (http://en.wikipedia.org/wiki/Lanczos_approximation):

Code:

<script type="text/javascript">
// Gamma approximation; coefficients used by the GNU Scientific Library
function gamma(z) {
  var p = [0.99999999999980993, 676.5203681218851, -1259.1392167224028, 771.32342877765313, -176.61502916214059, 12.507343278686905, -0.13857109526572012, 9.9843695780195716e-6, 1.5056327351493116e-7];
  if z < 0.5 {
     return Math.PI / (Math.sin(Math.PI*z) * gamma(1-z));
  } else {
    z -= 1;
    x = p[0];
    for (var i = 0; i < p.length; i++) x += p[i]/(z+i);
    t = z + p.length - 1.5;
    return Math.sqrt(2*Math.PI) * Math.pow(t, z+0.5) * Math.exp(-t) * x;
  }
}

for (var x = 0.1; x < 3; x += 0.1) document.write("x: " + x + " gamma(x): " + gamma(x) + "<br/>");
</script>

This returns an empty page, which usually means there is a syntactical error in the code. In the absence of a proper debugger, can anyone point out where this error might be?

Thank you in advance.

figaro

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LEARN ABOUT MOJAVE

math::bigint::fastcalc

Math::BigInt::FastCalc(3pm)				 Perl Programmers Reference Guide			       Math::BigInt::FastCalc(3pm)

NAME

       Math::BigInt::FastCalc - Math::BigInt::Calc with some XS for more speed

SYNOPSIS

       Provides support for big integer calculations. Not intended to be used by other modules. Other modules which sport the same functions can
       also be used to support Math::BigInt, like Math::BigInt::GMP or Math::BigInt::Pari.

DESCRIPTION

       In order to allow for multiple big integer libraries, Math::BigInt was rewritten to use library modules for core math routines. Any module
       which follows the same API as this can be used instead by using the following:

	       use Math::BigInt lib => 'libname';

       'libname' is either the long name ('Math::BigInt::Pari'), or only the short version like 'Pari'. To use this library:

	       use Math::BigInt lib => 'FastCalc';

       Note that from Math::BigInt v1.76 onwards, FastCalc will be loaded automatically, if possible.

STORAGE

       FastCalc works exactly like Calc, in stores the numbers in decimal form, chopped into parts.

METHODS

       The following functions are now implemented in FastCalc.xs:

	       _is_odd	       _is_even        _is_one	       _is_zero
	       _is_two	       _is_ten
	       _zero	       _one	       _two	       _ten
	       _acmp	       _len
	       _inc	       _dec
	       __strip_zeros   _copy

LICENSE

       This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

AUTHORS

       Original math code by Mark Biggar, rewritten by Tels <http://bloodgate.com/> in late 2000.  Separated from BigInt and shaped API with the
       help of John Peacock.

       Fixed, sped-up and enhanced by Tels http://bloodgate.com 2001-2003.  Further streamlining (api_version 1 etc.) by Tels 2004-2007.

       Bug-fixing by Peter John Acklam <pjacklam@online.no> 2010-2011.

SEE ALSO

       Math::BigInt, Math::BigFloat, Math::BigInt::GMP, Math::BigInt::FastCalc and Math::BigInt::Pari.

perl v5.18.2							    2014-01-06					       Math::BigInt::FastCalc(3pm)