include/selection/linearRankSelection.h

   1 #ifndef __SELECTION_LINEAR_RANK_H
   2 #define __SELECTION_LINEAR_RANK_H
   3
   4 #include <map>
   5
   6 #include "chromosome.h"
   7 #include "generation.h"
   8 #include "fitness/fitness.h"
   9 #include "selection/selection.h"
  10
  11 using namespace std;
  12
  13 namespace genetic {
  14 //     namespace selection {
  15         /**
  16          * Linear Rank Selection class.
  17          * Based on the
  18          */
  19         template < typename _Chromosome >
  20         class LinearRankSelection : public Selection<_Chromosome> {
  21         public:
  22             /**
  23              * Type representing Fitness function
  24              */
  25             typedef Fitness<_Chromosome> GeneticFitness;
  26
  27             /**
  28              * Value type returned by the Fitness function
  29              */
  30             typedef typename GeneticFitness::ValueType FitnessValueType;
  31         protected:
  32             /**
  33              * Type representing mapped Chromosome by its Rank value
  34              */
  35             typedef typename std::multimap<FitnessValueType, _Chromosome> ChromosomeMap;
  36
  37             /** Iterator for ChromosomeMap */
  38             typedef typename ChromosomeMap::iterator ChromosomeMapIterator;
  39
  40             /**
  41              * Calculates Ranks for the Chromosomes
  42              *
  43              * @return multimap containing ranked Chromosomes, where key is the
  44              *      rank value.
  45              */
  46             ChromosomeMap rankChromosomes() {
  47                 const unsigned int generationSize = this->generation.size();
  48                 FitnessValueType fitness = 0;
  49
  50                 ChromosomeMap generationFitness;
  51
  52                 for (unsigned int i = 0; i < generationSize; i++) {
  53                     fitness = this->checkChromosomeFitness(this->generation[i]);
  54                     generationFitness.insert(std::make_pair(fitness, this->generation[i]));
  55                 }
  56
  57                 // multimap is automatically sorted by key, so we don't need to
  58                 // sort it again
  59
  60                 // p(i) = (rank(i) / N*(N-1)), where rankedGeneration[i] = p(i)
  61                 ChromosomeMap rankedGeneration;
  62
  63                 unsigned int rank = generationSize;
  64                 const double denominator = generationSize * (generationSize - 1);
  65
  66                 for (ChromosomeMapIterator it = generationFitness.begin(); it != generationFitness.end(); it++) {
  67                     rankedGeneration.insert(std::make_pair(rank--/denominator, it->second));
  68                 }
  69
  70                 return rankedGeneration;
  71             }
  72
  73             /**
  74              * Invokes Selection calculations of the Linear Rank Selection
  75              *
  76              * @return new Generation of Chromosome's that passed the Selection
  77              */
  78             virtual Generation<_Chromosome> do_draw() {
  79                 ChromosomeMap probabilities = rankChromosomes();
  80
  81                 unsigned int size = probabilities.size();
  82                 const unsigned int denominator = size * (size - 1);
  83
  84                 std::vector<_Chromosome> selected;
  85
  86                 /** Random value used to draw chromosome */
  87                 FitnessValueType random = 0;
  88
  89                 while (size > 0) {
  90                     bool found = false;
  91                     random = (rand() % size) / (float)denominator;
  92
  93                     for (ChromosomeMapIterator it = probabilities.begin(); it != probabilities.end(); it++) {
  94                         if (random < it->first) {
  95                             found = true;
  96                             selected.push_back(it->second);
  97                             break;
  98                         }
  99                         // When NaN occur, just get first Chromosome
 100                         else if (it->first != it->first) {
 101                             selected.push_back(probabilities.begin()->second);
 102                             found = true;
 103                             break;
 104                         }
 105                     }
 106
 107                     if (found) {
 108                         size--;
 109                     }
 110                 }
 111
 112                 return Generation<_Chromosome>(selected);
 113             }
 114         public:
 115             LinearRankSelection(const Generation<_Chromosome>& _generation, GeneticFitness& _fitness) :
 116                 Selection<_Chromosome>(_generation, _fitness) {
 117             }
 118         };
 119 //     }
 120 }
 121
 122 #endif /* __SELECTION_LINEAR_RANK_H */