chi2_inl.h

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/**
 *
 *   Copyright (c) 2005-2021 by Pierre-Henri WUILLEMIN(@LIP6) & Christophe GONZALES(@AMU)
 *   info_at_agrum_dot_org
 *
 *  This library is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this library.  If not, see <http://www.gnu.org/licenses/>.
 *
 */


/**
 * @file
 * @brief The class that represents the chi2 distribution
 *
 * The Chi2 class allows to easily compute critical values for the Chi2
 * distribution.
 *
 * @author Christophe GONZALES(@AMU) and Pierre-Henri WUILLEMIN(@LIP6)
 */


namespace gum {

  // sets the conditioning nodes (useful for computing degrees of freedom)
  INLINE void Chi2::setConditioningNodes(const std::vector< Idx >& db_conditioning_ids) {
    _conditioning_size_ = 1;
    for (Idx i = 0; i < db_conditioning_ids.size(); ++i) {
      _conditioning_size_ *= _modalities_[db_conditioning_ids[i]];
    }
  }

  // returns the number of degrees of freedom
  INLINE Size Chi2::degreesOfFreedom(const std::pair< Idx, Idx >& pair) {
    return degreesOfFreedom(pair.first, pair.second);
  }

  // returns the number of degrees of freedom
  INLINE Size Chi2::degreesOfFreedom(Idx var1, Idx var2) {
    return (_conditioning_size_ * (_modalities_[var1] - 1) * (_modalities_[var2] - 1));
  }

  // computes the critical value according to the number of degrees of freedom
  ALWAYS_INLINE double Chi2::criticalValue(const std::pair< Idx, Idx >& pair) {
    return criticalValue(pair.first, pair.second);
  }

  // computes the critical value according to the number of degrees of freedom
  ALWAYS_INLINE double Chi2::criticalValue(Idx var1, Idx var2) {
    Size DF = degreesOfFreedom(var1, var2);

    // try to see if the threshold is not already in cache
    try {
      return _critical_values_[DF];
    } catch (const Exception&) {
      // here we have to compute the threshold of the chi2
      // we use Gary Perlman's algorithm
      double value = _criticalValue_(_confidence_proba_, DF);
      _critical_values_.insert(DF, value);
      return value;
    }
  }

  // modifies the confidence proba
  INLINE void Chi2::setConfidenceProba(double new_proba) {
    // if we did not change the confidence proba, do nothing
    if (_confidence_proba_ == new_proba) return;

    _confidence_proba_ = new_proba;

    // remove the currently stored critical values
    _critical_values_.clear();
  }

} /* namespace gum */