PermLib
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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 RANDOMSCHREIERSIMSCONSTRUCTION_H_ 00034 #define RANDOMSCHREIERSIMSCONSTRUCTION_H_ 00035 00036 #include <permlib/construct/base_construction.h> 00037 #include <permlib/generator/random_generator.h> 00038 #include <permlib/bsgs.h> 00039 00040 #include <boost/foreach.hpp> 00041 00042 namespace permlib { 00043 00045 00049 template <class PERM, class TRANS> 00050 class RandomSchreierSimsConstruction : public BaseConstruction<PERM, TRANS> { 00051 public: 00053 00058 RandomSchreierSimsConstruction(unsigned int n, RandomGenerator<PERM> *rng, unsigned long knownOrder = 0); 00059 00061 00063 template <class ForwardIterator> 00064 BSGS<PERM, TRANS> construct(ForwardIterator generatorsBegin, ForwardIterator generatorsEnd, bool& guaranteedBSGS) const; 00065 00067 00077 template <class ForwardIterator, class InputIterator> 00078 BSGS<PERM, TRANS> construct(ForwardIterator generatorsBegin, ForwardIterator generatorsEnd, InputIterator prescribedBaseBegin, InputIterator prescribedBaseEnd, bool& guaranteedBSGS) const; 00079 00081 mutable unsigned int m_statRandomElementsConsidered; 00082 00084 static const unsigned int minimalConsecutiveSiftingElementCount = 20; 00085 00087 static const unsigned int maxIterationFactor = 10000; 00088 private: 00089 RandomGenerator<PERM> *m_rng; 00090 unsigned long m_knownOrder; 00091 }; 00092 00093 // 00094 // ---- IMPLEMENTATION 00095 // 00096 00097 template <class PERM, class TRANS> 00098 RandomSchreierSimsConstruction<PERM,TRANS>::RandomSchreierSimsConstruction(unsigned int n, RandomGenerator<PERM> *rng, unsigned long knownOrder) 00099 : BaseConstruction<PERM, TRANS>(n), m_statRandomElementsConsidered(0), m_rng(rng), m_knownOrder(knownOrder) 00100 { } 00101 00102 template <class PERM, class TRANS> 00103 template <class ForwardIterator> 00104 inline BSGS<PERM, TRANS> RandomSchreierSimsConstruction<PERM,TRANS>::construct(ForwardIterator generatorsBegin, ForwardIterator generatorsEnd, bool& guaranteedBSGS) const { 00105 return construct(generatorsBegin, generatorsEnd, BaseConstruction<PERM,TRANS>::empty, BaseConstruction<PERM,TRANS>::empty, guaranteedBSGS); 00106 } 00107 00108 template <class PERM, class TRANS> 00109 template <class ForwardIterator, class InputIterator> 00110 BSGS<PERM, TRANS> RandomSchreierSimsConstruction<PERM, TRANS> 00111 ::construct(ForwardIterator generatorsBegin, ForwardIterator generatorsEnd, InputIterator prescribedBaseBegin, InputIterator prescribedBaseEnd, bool& guaranteedBSGS) const 00112 { 00113 const unsigned int &n = BaseConstruction<PERM, TRANS>::m_n; 00114 BSGS<PERM, TRANS> ret(n); 00115 std::vector<dom_int> &B = ret.B; 00116 std::vector<TRANS> &U = ret.U; 00117 std::vector<std::list<typename PERM::ptr> > S; 00118 setup(generatorsBegin, generatorsEnd, prescribedBaseBegin, prescribedBaseEnd, ret, S); 00119 00120 unsigned int consecutiveSiftingElementCount = minimalConsecutiveSiftingElementCount; 00121 if (m_knownOrder > 0) 00122 // remove consecutive sifting limit if we have the group order as Las Vegas-abort criterion 00123 consecutiveSiftingElementCount = maxIterationFactor; 00124 const unsigned int maxIterationCount = B.size() * maxIterationFactor; 00125 for (unsigned int it = 0; it < maxIterationCount; ++it) { 00126 bool isProbableBSGS = true; 00127 for (unsigned int i = 0; i < consecutiveSiftingElementCount && ret.order() != m_knownOrder; ++i) { 00128 PERM g = m_rng->next(); 00129 ++m_statRandomElementsConsidered; 00130 PERM h(n); 00131 unsigned int j = ret.sift(g, h); 00132 if (j < B.size() || !h.isIdentity()) { 00133 // flush it, because we add it as a generator 00134 h.flush(); 00135 00136 if (j == B.size()) { 00137 dom_int gamma = n+1; 00138 if (ret.chooseBaseElement(h, gamma)) { 00139 B.push_back(gamma); 00140 } 00141 BOOST_ASSERT(j < B.size()); 00142 S.push_back(std::list<typename PERM::ptr>()); 00143 U.push_back(TRANS(n)); 00144 } 00145 00146 boost::shared_ptr<PERM> hPtr(new PERM(h)); 00147 S[j].insert(S[j].end(), hPtr); 00148 00149 ret.orbitUpdate(j, S[j], hPtr); 00150 isProbableBSGS = false; 00151 break; 00152 } 00153 } 00154 if (isProbableBSGS) 00155 break; 00156 } 00157 00158 mergeGenerators(S, ret); 00159 00160 // convinience check of group order 00161 guaranteedBSGS = ret.order() == m_knownOrder; 00162 00163 return ret; 00164 } 00165 00166 } 00167 00168 #endif // -- RANDOMSCHREIERSIMSCONSTRUCTION_H_