eoRanking.h

//-----------------------------------------------------------------------------

#ifndef eoRanking_h
#define eoRanking_h

#include <eoPerf2Worth.h>

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