permlib  0.2.6
Library for permutation computations
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include/permlib/generator/random_schreier_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
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00028 // THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00029 //
00030 // ---------------------------------------------------------------------------
00031 
00032 
00033 #ifndef RANDOMSCHREIERGENERATOR_H_
00034 #define RANDOMSCHREIERGENERATOR_H_
00035 
00036 #include <permlib/generator/random_generator.h>
00037 
00038 namespace permlib {
00039 
00041 
00045 template <class PERM,class TRANS>
00046 class RandomSchreierGenerator : public RandomGenerator<PERM> {
00047 public:
00049 
00054         RandomSchreierGenerator(const BSGS<PERM,TRANS> &bsgs, unsigned int i, const TRANS &U);
00055         virtual PERM next();
00056 private:
00057         const BSGS<PERM,TRANS> &m_bsgs;
00058         unsigned int m_i;
00059         const TRANS &m_U;
00060 };
00061 
00062 //
00063 //     ----       IMPLEMENTATION
00064 //
00065 
00066 template <class PERM,class TRANS>
00067 RandomSchreierGenerator<PERM,TRANS>::RandomSchreierGenerator(const BSGS<PERM,TRANS> &bsgs, unsigned int i, const TRANS &U) 
00068         : m_bsgs(bsgs), m_i(i), m_U(U) 
00069 { }
00070 
00071 template <class PERM,class TRANS>
00072 PERM RandomSchreierGenerator<PERM,TRANS>::next() { 
00073         PERM g = m_bsgs.random(m_i);
00074         boost::scoped_ptr<PERM> u_g(m_U.at(g / m_bsgs.B[m_i]));
00075         u_g->invertInplace();
00076         g *= *u_g;
00077         return g;
00078 }
00079 
00080 }
00081 
00082 #endif // -- RANDOMSCHREIERGENERATOR_H_