# eoStochasticUniversalSelect.h

    00001 // -*- mode: c++; c-indent-level: 4; c++-member-init-indent: 8; comment-column: 35; -*-
    00002
    00003 //-----------------------------------------------------------------------------
    00004 // eoStochasticUniversalSelect.h
    00005 // (c) Maarten Keijzer 2003
    00006 /*
    00007     This library is free software; you can redistribute it and/or
    00008     modify it under the terms of the GNU Lesser General Public
    00009     License as published by the Free Software Foundation; either
    00010     version 2 of the License, or (at your option) any later version.
    00011
    00012     This library is distributed in the hope that it will be useful,
    00013     but WITHOUT ANY WARRANTY; without even the implied warranty of
    00014     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    00015     Lesser General Public License for more details.
    00016
    00017     You should have received a copy of the GNU Lesser General Public
    00018     License along with this library; if not, write to the Free Software
    00019     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    00020
    00021     Contact: todos@geneura.ugr.es, http://geneura.ugr.es
    00022              Marc.Schoenauer@polytechnique.fr
    00023              mkeijzer@cs.vu.nl
    00024  */
    00025 //-----------------------------------------------------------------------------
    00026
    00027 #ifndef eoStochasticUniversalSelect_h
    00028 #define eoStochasticUniversalSelect_h
    00029
    00030 //-----------------------------------------------------------------------------
    00031
    00032 #include <utils/eoRNG.h>
    00033 #include <eoSelectOne.h>
    00034 #include <utils/selectors.h>
    00035 #include <eoPop.h>
    00036
    00037 //-----------------------------------------------------------------------------
    00042 //-----------------------------------------------------------------------------
    00043
    00044 template <class EOT> class eoStochasticUniversalSelect: public eoSelectOne<EOT>
    00045 {
    00046 public:
    00048   eoStochasticUniversalSelect(const eoPop<EOT>& pop = eoPop<EOT>())
    00049   {
    00050     if (minimizing_fitness<EOT>())
    00051       throw std::logic_error("eoStochasticUniversalSelect: minimizing fitness");
    00052   }
    00053
    00054   void setup(const eoPop<EOT>& _pop)
    00055   {
    00056       if (_pop.size() == 0) return;
    00057
    00058       std::vector<typename EOT::Fitness> cumulative(_pop.size());
    00059
    00060       cumulative[0] = _pop[0].fitness();
    00061       for (unsigned i = 1; i < _pop.size(); ++i)
    00062       {
    00063           cumulative[i] = _pop[i].fitness() + cumulative[i-1];
    00064       }
    00065
    00066       indices.reserve(_pop.size());
    00067       indices.resize(0);
    00068
    00069       double fortune = rng.uniform() * cumulative.back();
    00070       double step = cumulative.back() / double(_pop.size());
    00071
    00072       unsigned i = std::upper_bound(cumulative.begin(), cumulative.end(), fortune) - cumulative.begin();
    00073
    00074       while (indices.size() < _pop.size()) {
    00075
    00076           while (cumulative[i] < fortune) {i++;} // linear search is good enough as we average one step each time
    00077
    00078           indices.push_back(i);
    00079           fortune += step;
    00080           if (fortune >= cumulative.back()) { // start at the beginning
    00081               fortune -= cumulative.back();
    00082               i = 0;
    00083           }
    00084       }
    00085       // shuffle
    00086       for (int i = indices.size() - 1; i > 0; --i) {
    00087           int j = rng.random(i+1);
    00088           std::swap(indices[i], indices[j]);
    00089       }
    00090   }
    00091
    00094   const EOT& operator()(const eoPop<EOT>& _pop)
    00095   {
    00096       if (indices.empty()) setup(_pop);
    00097
    00098       unsigned index = indices.back();
    00099       indices.pop_back();
    00100       return _pop[index];
    00101   }
    00102
    00103 private :
    00104
    00105   typedef std::vector<unsigned> IndexVec;
    00106   IndexVec indices;
    00107 };
    00108
    00109 #endif