IncompleteGammaComplement.cc

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#include "CommonTools/Statistics/src/IncompleteGammaComplement.h"
#include "CommonTools/Statistics/src/GammaContinuedFraction.h"
#include "CommonTools/Statistics/src/GammaSeries.h"
#include "CommonTools/Statistics/src/GammaLn.h"

#include "FWCore/MessageLogger/interface/MessageLogger.h"

#include <iostream>
#include <cmath>

float IncompleteGammaComplement::value(float a, float x) {
  if (x < 0.0 || a <= 0.0)
    edm::LogInfo("IncompleteGammaComplement") << "IncompleteGammaComplement::invalid arguments";
  if (x < (a + 1.0))
    // take the complement of the series representation
    return 1. - GammaSeries(a, x) * (exp(-x + a * log(x) - GammaLn(a)));
  else
    // use the continued fraction representation
    return GammaContinuedFraction(a, x) * (exp(-x + a * log(x) - GammaLn(a)));
}

float IncompleteGammaComplement::ln(float a, float x) {
  if (x < 0.0 || a <= 0.0)
    edm::LogInfo("IncompleteGammaComplement") << "IncompleteGammaComplement::invalid arguments";
  if (x < (a + 1.0))
    // take the complement of the series representation
    return log(1. - GammaSeries(a, x) * (exp(-x + a * log(x) - GammaLn(a))));
  else
    // use the continued fraction representation
    return log(GammaContinuedFraction(a, x)) - x + a * log(x) - GammaLn(a);
}