/*

(c) Thales group, 2010

    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;
    version 2 of the License.

    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, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

Contact: http://eodev.sourceforge.net

Authors:
Lionel Parreaux <lionel.parreaux@gmail.com>

*/

#ifndef moFitnessVarianceStat_h
#define moFitnessVarianceStat_h

#include <continuator/moStat.h>

/**
 * Statistic that incrementally computes the variance of the fitness of the solutions during the search
 */
template <class EOT>
class moFitnessVarianceStat : public moStat<EOT, typename EOT::Fitness>
{
public :
    typedef typename EOT::Fitness Fitness;
    using moStat< EOT , typename EOT::Fitness >::value;

    /**
     * Default Constructor
     * @param _reInitSol when true the best so far is reinitialized
     */
    moFitnessVarianceStat(bool _reInitSol = true)
    : moStat<EOT, typename EOT::Fitness>(Fitness(), "var"),
      reInitSol(_reInitSol), firstTime(true),
      nbSolutionsEncountered(0), currentAvg(0), currentVar(0)
    { }
    
    /**
     * Initialization of the best solution on the first one
     * @param _sol the first solution
     */
    virtual void init(EOT & _sol) {
        if (reInitSol || firstTime)
        {
            value() = 0.0;
            nbSolutionsEncountered = currentAvg = currentVar = 0;
            firstTime = false;
        }
    	  operator()(_sol);
    }

  /**
   * Update the best solution
   * @param _sol the current solution
   */
  virtual void operator()(EOT & _sol) {
      ++nbSolutionsEncountered;
      double x = _sol.fitness();
      double oldAvg = currentAvg;
      currentAvg = oldAvg + (x - oldAvg)/nbSolutionsEncountered;
      double oldVar = currentVar;
      currentVar = oldVar + (x - oldAvg) * (x - currentAvg);
      value() = currentVar/nbSolutionsEncountered;
  }

    /**
     * @return name of the class
     */
    virtual std::string className(void) const {
        return "moFitnessVarianceStat";
    }

protected:
    bool reInitSol;
    bool firstTime;
    double
      nbSolutionsEncountered
    , currentAvg
    , currentVar // actually the var * n
    ;

};

#endif // moFitnessVarianceStat_h