GammaLn.cc File Reference

#include "CommonTools/Statistics/src/GammaLn.h"
#include <cmath>

Go to the source code of this file.

Functions
float	GammaLn (float z)

Function Documentation

GammaLn()

float GammaLn

(

float

z

)

Returns the value ln( gamma(z) ) for z > 0

Definition at line 4 of file GammaLn.cc.

References CrabHelper::log, groupFilesInBlocks::temp, relval_data_highstats::y, and ctppsOpticalFunctions_non_DB_cff::z.

Referenced by IncompleteGammaComplement::ln(), and IncompleteGammaComplement::value().

                       {
  const static double coefficients[6] = {76.18009172947146,
                                         -86.50532032941677,
                                         24.01409824083091,
                                         -1.231739572450155,
                                         0.1208650973866179e-2,
                                         -0.5395239384953e-5};

  double temp = z + 5.5;
  temp -= (z + 0.5) * log(temp);
  double y = z;
  double series = 1.000000000190015;
  for (int term = 0; term < 6; term++)
    series += coefficients[term] / ++y;
  return -temp + log(2.5066282746310005 * series / z);
}