Upsilon/apps/probability/law/normal_law.cpp

#include "normal_law.h"
#include "erf_inv.h"
#include <assert.h>
#include <cmath>
#include <float.h>
#include <ion.h>

namespace Probability {

float NormalLaw::yMax() const {
  float maxAbscissa = m_parameter1;
  float result = evaluateAtAbscissa(maxAbscissa);
  if (std::isnan(result) || result <= 0.0f) {
    result = 1.0f;
  }
  return result * (1.0f + k_displayTopMarginRatio);
}

I18n::Message NormalLaw::parameterNameAtIndex(int index) {
  if (index == 0) {
    return I18n::Message::Mu;
  }
  assert(index == 1);
  return I18n::Message::Sigma;
}

I18n::Message NormalLaw::parameterDefinitionAtIndex(int index) {
  if (index == 0) {
    return I18n::Message::MeanDefinition;
  }
  assert(index == 1);
  return I18n::Message::DeviationDefinition;
}

float NormalLaw::evaluateAtAbscissa(float x) const {
  if (m_parameter2 == 0.0f) {
    return NAN;
  }
  return (1.0f/(std::fabs(m_parameter2) * std::sqrt(2.0f * M_PI))) * std::exp(-0.5f * std::pow((x - m_parameter1)/m_parameter2, 2));
}

bool NormalLaw::authorizedValueAtIndex(float x, int index) const {
  if (index == 0) {
    return true;
  }
  if (x <= FLT_MIN || std::fabs(m_parameter1/x) > k_maxRatioMuSigma) {
    return false;
  }
  return true;
}

void NormalLaw::setParameterAtIndex(float f, int index) {
  TwoParameterLaw::setParameterAtIndex(f, index);
  if (index == 0 && std::fabs(m_parameter1/m_parameter2) > k_maxRatioMuSigma) {
    m_parameter2 = m_parameter1/k_maxRatioMuSigma;
  }
}

double NormalLaw::cumulativeDistributiveFunctionAtAbscissa(double x) const {
  if (m_parameter2 == 0.0f) {
    return NAN;
  }
  return standardNormalCumulativeDistributiveFunctionAtAbscissa((x-m_parameter1)/std::fabs(m_parameter2));
}

double NormalLaw::cumulativeDistributiveInverseForProbability(double * probability) {
  if (m_parameter2 == 0.0f) {
    return NAN;
  }
  return standardNormalCumulativeDistributiveInverseForProbability(*probability) * std::fabs(m_parameter2) + m_parameter1;
}

double NormalLaw::standardNormalCumulativeDistributiveFunctionAtAbscissa(double abscissa) const {
  if (abscissa == 0.0) {
    return 0.5;
  }
  if (abscissa < 0.0) {
    return 1.0 - standardNormalCumulativeDistributiveFunctionAtAbscissa(-abscissa);
  }
  if (abscissa > k_boundStandardNormalDistribution) {
    return 1.0;
  }
  return 0.5 + 0.5 * std::erf(abscissa/std::sqrt(2.0));
}

double NormalLaw::standardNormalCumulativeDistributiveInverseForProbability(double probability) {
  if (probability >= 1.0) {
    return INFINITY;
  }
  if (probability <= 0.0) {
    return -INFINITY;
  }
  if (probability < 0.5) {
    return -standardNormalCumulativeDistributiveInverseForProbability(1-probability);
  }
  return std::sqrt(2.0) * erfInv(2.0 * probability - 1.0);
}

float NormalLaw::xExtremum(bool min) const {
  int coefficient = (min ? -1 : 1);
  if (m_parameter2 == 0.0f) {
    return m_parameter1 + coefficient * 1.0f;
  }
  return m_parameter1 + coefficient * 5.0f * std::fabs(m_parameter2);
}

}