permlib  0.2.6
Library for permutation computations
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include/permlib/transversal/schreier_tree_transversal.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,
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00028 // THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00029 //
00030 // ---------------------------------------------------------------------------
00031 
00032 
00033 #ifndef SCHREIERTRANSVERSAL_H_
00034 #define SCHREIERTRANSVERSAL_H_
00035 
00036 #include <permlib/transversal/transversal.h>
00037 
00038 namespace permlib {
00039 
00040 namespace exports { struct BSGSSchreierExport; struct BSGSSchreierImport; }
00041 
00043 template <class PERM>
00044 class SchreierTreeTransversal : public Transversal<PERM> {
00045 public:
00047         SchreierTreeTransversal(unsigned int n);
00048 
00049     virtual bool trivialByDefinition(const PERM& x, unsigned long to) const;
00050     virtual PERM* at(unsigned long val) const;
00051         
00052         virtual void updateGenerators(const std::map<PERM*,typename PERM::ptr>& generatorChange);
00053         
00055 
00059         SchreierTreeTransversal<PERM> clone(const std::map<PERM*,typename PERM::ptr>& generatorChange) const;
00060         
00062     mutable unsigned int m_statMaxDepth;
00063 protected:
00064     virtual void registerMove(unsigned long from, unsigned long to, const typename PERM::ptr &p);
00065         
00066         friend struct permlib::exports::BSGSSchreierExport;
00067         friend struct permlib::exports::BSGSSchreierImport;
00068 };
00069 
00070 //
00071 //     ----       IMPLEMENTATION
00072 //
00073 
00074 template <class PERM>
00075 SchreierTreeTransversal<PERM>::SchreierTreeTransversal(unsigned int n_) 
00076         : Transversal<PERM>(n_), m_statMaxDepth(0) 
00077 { }
00078 
00079 template <class PERM>
00080 bool SchreierTreeTransversal<PERM>::trivialByDefinition(const PERM& x, unsigned long to) const {
00081         return *Transversal<PERM>::m_transversal[to] == x; 
00082 }
00083 
00084 template <class PERM>
00085 void SchreierTreeTransversal<PERM>::registerMove(unsigned long from, unsigned long to, const typename PERM::ptr &p) {
00086         Transversal<PERM>::registerMove(from, to, p);
00087         Transversal<PERM>::m_transversal[to] = p;
00088 }
00089 
00090 
00091 template <class PERM>
00092 PERM* SchreierTreeTransversal<PERM>::at(unsigned long val) const {
00093         const std::vector<boost::shared_ptr<PERM> > &transversal = Transversal<PERM>::m_transversal;
00094 
00095         if (transversal[val] == 0) {
00096                 return 0;
00097         }
00098 
00099         unsigned int depth = 1;
00100         PERM *res = new PERM(*transversal[val]);
00101         const PERM* inv = 0;
00102         //std::cout << "Schreier " << *res << std::endl;
00103         unsigned long pred = *res % val;
00104         //TODO: reserve space for PermutationWord-res beforehand (we know how long the m_word vector will be)
00105         while (pred != val) {
00106                 inv = transversal[pred].get();
00107                 BOOST_ASSERT(inv);
00108                 PERMLIB_DEBUG(std::cout << "Schreier2 " << inv << " / " << val << " , " << pred << std::endl;)
00109                 *res ^= *inv;
00110                 val = pred;
00111                 pred = *inv % pred;
00112                 ++depth;
00113         }
00114         m_statMaxDepth = std::max(m_statMaxDepth, depth);
00115         //std::cout << "Schreier3 " << *res << std::endl;
00116         return res;
00117 }
00118 
00119 template <class PERM>
00120 void SchreierTreeTransversal<PERM>::updateGenerators(const std::map<PERM*,typename PERM::ptr>& generatorChange) {
00121         unsigned int missedCount = 0;
00122         BOOST_FOREACH(typename PERM::ptr& p, this->m_transversal) {
00123                 if (!p)
00124                         continue;
00125                 //std::cout << "require " << p.get() << std::endl;
00126                 typename std::map<PERM*,typename PERM::ptr>::const_iterator pIt = generatorChange.find(p.get());
00127                 //BOOST_ASSERT( pIt != generatorChange.end() );
00128                 if (pIt != generatorChange.end()) {
00129                         p = (*pIt).second;
00130                 } else {
00131                         ++missedCount;
00132                         //std::cout << "missed " << p.get() << " = " << *p << std::endl;
00133                 }
00134         }
00135         // we always miss the identity -- and not anything else
00136         BOOST_ASSERT( missedCount == 1 );
00137 }
00138 
00139 template <class PERM>
00140 SchreierTreeTransversal<PERM> SchreierTreeTransversal<PERM>::clone(const std::map<PERM*,typename PERM::ptr>& generatorChange) const {
00141         SchreierTreeTransversal<PERM> ret(*this);
00142         ret.updateGenerators(generatorChange);
00143         return ret;
00144 }
00145 
00146 }
00147 
00148 #endif // -- SCHREIERTRANSVERSAL_H_