include "NSLog.incl"

#define FB_M_E 2.7182818284590452

double local fn StirlingGamma( x as double )
  return fn sqrt(2 * M_PI / x ) * fn pow(x / FB_M_E, x )
end fn = 0.0

double local fn LanczosGamma( x as double )
  int g = 7
  static double p(8) = {0.99999999999980993, 676.5203681218851, -1259.1392167224028,¬
  771.32342877765313, -176.61502916214059, 12.507343278686905, -0.13857109526572012,¬
  9.9843695780195716e-6, 1.5056327351493116e-7}

  if ( x < 0.5 ) then return M_PI / ( sin( M_PI * x ) * fn LanczosGamma( 1 - x ) )
  x -= 1.0
  double a = p(0)
  for int i = 1 to 8
    a += p(i) / ( x + i )
  next
  double t = x + g + 0.5
  return fn sqrt(2 * M_PI ) * fn pow(t, x + 0.5 ) * exp(-t ) * a
end fn = 0.0

void local fn RunGammaFunctions
  NSLog( @"Gamma\tStirling\t\t\t Lanczos" )
  for double i = 1.0 to 20
    double value = i / 10.0
    NSLog( @"%1.2f\t%17.15f\t %1.15f", value, fn StirlingGamma( value ), fn LanczosGamma( value ) )
  next
end fn

fn RunGammaFunctions

HandleEvents