permlib  0.2.6
Library for permutation computations
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include/permlib/generator/product_replacement_generator.h
00001 // ---------------------------------------------------------------------------
00002 //
00003 //  This file is part of PermLib.
00004 //
00005 // Copyright (c) 2009-2011 Thomas Rehn <thomas@carmen76.de>
00006 // All rights reserved.
00007 // 
00008 // Redistribution and use in source and binary forms, with or without
00009 // modification, are permitted provided that the following conditions
00010 // are met:
00011 // 1. Redistributions of source code must retain the above copyright
00012 //    notice, this list of conditions and the following disclaimer.
00013 // 2. Redistributions in binary form must reproduce the above copyright
00014 //    notice, this list of conditions and the following disclaimer in the
00015 //    documentation and/or other materials provided with the distribution.
00016 // 3. The name of the author may not be used to endorse or promote products
00017 //    derived from this software without specific prior written permission.
00018 // 
00019 // THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
00020 // IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
00021 // OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
00022 // IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
00023 // INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
00024 // NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
00025 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
00026 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
00027 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
00028 // THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00029 //
00030 // ---------------------------------------------------------------------------
00031 
00032 
00033 #ifndef PRODUCTREPLACEMENTGENERATOR_H
00034 #define PRODUCTREPLACEMENTGENERATOR_H
00035 
00036 #include <permlib/generator/random_generator.h>
00037 
00038 #include <vector>
00039 #include <boost/iterator/indirect_iterator.hpp>
00040 
00041 namespace permlib {
00042 
00044 template <class PERM>
00045 class ProductReplacementGenerator : public RandomGenerator<PERM> {
00046 public:
00048 
00052         template <class InputIterator>
00053         ProductReplacementGenerator(const unsigned int n, InputIterator generatorsBegin, InputIterator generatorsEnd);
00054         
00055         virtual PERM next();
00056 private:
00057         std::vector<PERM> m_generators;
00058         const unsigned int m_n;
00059 };
00060 
00061 //
00062 //     ----       IMPLEMENTATION
00063 //
00064 
00065 template <class PERM>
00066 template <class InputIterator>
00067 ProductReplacementGenerator<PERM>::ProductReplacementGenerator(const unsigned int n, InputIterator generatorsBegin, InputIterator generatorsEnd) 
00068         : m_generators(boost::indirect_iterator<InputIterator, PERM>(generatorsBegin), 
00069                                    boost::indirect_iterator<InputIterator, PERM>(generatorsEnd)),
00070                 m_n(n)
00071 {
00072         const unsigned int additionalElements = 10;
00073         const unsigned int oldSize = m_generators.size();
00074         const unsigned int replacementRounds = std::max(oldSize * 10, static_cast<unsigned int>(100));
00075         if (oldSize == 0)
00076                 return;
00077         
00078         m_generators.reserve(oldSize + additionalElements + 1);
00079         for (unsigned int i = 0; i < additionalElements; ++i) {
00080                 m_generators.push_back(m_generators[randomInt(oldSize)]);
00081         }
00082         m_generators.push_back(PERM(m_generators[0].size()));
00083         
00084         for (unsigned int k = 0; k < replacementRounds; ++k) {
00085                 next();
00086         }
00087 }
00088 
00089 template <class PERM>
00090 PERM ProductReplacementGenerator<PERM>::next() {
00091         if (m_generators.size() == 0) {
00092                 return PERM(m_n);
00093         }
00094         
00095         unsigned int i = randomInt(m_generators.size() - 1);
00096         unsigned int j = randomInt(m_generators.size() - 2);
00097         if (j >= i) ++j;
00098         switch (randomInt(4)) {
00099         case 0:
00100                 m_generators[i] *=  m_generators[j]; break;
00101         case 1:
00102                 m_generators[i] *= ~m_generators[j]; break;
00103         case 2:
00104                 m_generators[i] ^=  m_generators[j]; break;
00105         case 3:
00106                 m_generators[i] ^= ~m_generators[j]; break;
00107         }
00108         m_generators[m_generators.size()-1] *= m_generators[i];
00109         return m_generators[m_generators.size()-1];
00110 }
00111 
00112 }
00113 
00114 #endif // -- PRODUCTREPLACEMENTGENERATOR_H