eoLinearFitScaling.h

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

#ifndef eoLinearFitScaling_h
#define eoLinearFitScaling_h

#include <eoSelectFromWorth.h>
#include <eoPerf2Worth.h>

template <class EOT>
class eoLinearFitScaling : 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)
    */
    eoLinearFitScaling(double _p=2.0)
        : pressure(_p) {}

    /* COmputes the ranked fitness: fitnesses range in [m,M]
       with m=2-pressure/popSize and M=pressure/popSize.
       in between, the progression depends on exponent (linear if 1).
    */
    virtual void operator()(const eoPop<EOT>& _pop) {
        unsigned pSize =_pop.size();
        // value() refers to the vector of worthes (we're in an eoParamvalue)
        value().resize(pSize);

        // best and worse fitnesses
        double bestFitness = static_cast<double> (_pop.best_element().fitness());
        //    double worstFitness = static_cast<double> (_pop.worse_element().fitness());

        // average fitness
        double sum=0.0;
        unsigned i;
        for (i=0; i<pSize; i++)
            sum += static_cast<double>(_pop[i].fitness());
        double averageFitness = sum/pSize;

        // the coefficients for linear scaling
        double denom = pSize*(bestFitness - averageFitness);
        double alpha = (pressure-1)/denom;
        double beta = (bestFitness - pressure*averageFitness)/denom;

        for (i=0; i<pSize; i++) { // truncate to 0
            value()[i] = std::max(alpha*_pop[i].fitness()+beta, 0.0);
        }
    }

private:
    double pressure;    // selective pressure
};



#endif

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