eoranking.h

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/** -*- mode: c++; c-indent-level: 4; c++-member-init-indent: 8; comment-column: 35; -*-

   -----------------------------------------------------------------------------
   eoRanking.h
   (c) Maarten Keijzer, Marc Schoenauer, 2001

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

    Contact: [e-mail], http://geneura.ugr.es
             [e-mail]
             [e-mail]
 */
//-----------------------------------------------------------------------------

#ifndef eoRanking_h
#define eoRanking_h

#include <eoPerf2Worth.h>

/** An instance of eoPerfFromWorth
 *  COmputes the ranked fitness: fitnesses range in [m,M]
 *  with m=2-pressure/popSize and M=pressure/popSize.
 *  in between, the progression depstd::ends on exponent (linear if 1).
 */
template <class EOT>
class eoRanking : public eoPerf2Worth<EOT> // false: do not cache fitness
{
public:

    using eoPerf2Worth<EOT>::value;

  /* Ctor:
   @param _p selective pressure (in (1,2]
   @param _e exponent (1 == linear)
  */
  eoRanking(double _p=2.0, double _e=1.0):
    pressure(_p), exponent(_e) {}

  /* helper function: finds index in _pop of _eo, an EOT * */
  int lookfor(const EOT *_eo, const eoPop<EOT>& _pop)
    {
      typename eoPop<EOT>::const_iterator it;
      for (it=_pop.begin(); it<_pop.end(); it++)
	{
	  if (_eo == &(*it))
	    return it-_pop.begin();
	}
      throw std::runtime_error("Not found in eoLinearRanking");
    }

  /* COmputes the ranked fitness: fitnesses range in [m,M]
     with m=2-pressure/popSize and M=pressure/popSize.
     in between, the progression depstd::ends on exponent (linear if 1).
   */
  virtual void operator()(const eoPop<EOT>& _pop)
    {
      std::vector<const EOT *> rank;
      _pop.sort(rank);
      unsigned pSize =_pop.size();
      unsigned int pSizeMinusOne = pSize-1;

      if (pSize <= 1)
	throw std::runtime_error("Cannot do ranking with population of size <= 1");

      // value() refers to the std::vector of worthes (we're in an eoParamvalue)
      value().resize(pSize);

      double beta = (2-pressure)/pSize;
      if (exponent == 1.0)	   // no need for exponetial then
	{
	  double alpha = (2*pressure-2)/(pSize*pSizeMinusOne);
	  for (unsigned i=0; i<pSize; i++)
	    {
	      int which = lookfor(rank[i], _pop);
	      value()[which] = alpha*(pSize-i)+beta; // worst -> 1/[P(P-1)/2]
	    }
	}
      else				   // exponent != 1
	{
	  double gamma = (2*pressure-2)/pSize;
	  for (unsigned i=0; i<pSize; i++)
	    {
	      int which = lookfor(rank[i], _pop);
	      // value in in [0,1]
	      double tmp = ((double)(pSize-i))/pSize;
	      // to the exponent, and back to [m,M]
	      value()[which] = gamma*pow(tmp, exponent)+beta;
	    }
	}
    }
 private:
  double pressure;	// selective pressure
  double exponent;
};



#endif