permlib  0.2.6
Library for permutation computations
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include/permlib/predicate/group_intersection_predicate.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
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00030 // ---------------------------------------------------------------------------
00031 
00032 
00033 #ifndef GROUPINTERSECTIONPREDICATE_H_
00034 #define GROUPINTERSECTIONPREDICATE_H_
00035 
00036 #include <permlib/bsgs.h>
00037 #include <permlib/predicate/subgroup_predicate.h>
00038 
00039 #include <boost/foreach.hpp>
00040 
00041 namespace permlib {
00042 
00044 template <class PERM, class TRANS>
00045 class GroupIntersectionPredicate : public SubgroupPredicate<PERM> {
00046 public:
00048 
00052         GroupIntersectionPredicate(const BSGS<PERM, TRANS> &g, const BSGS<PERM, TRANS> &h);
00053 
00054         virtual bool operator()(const PERM &p) const;
00055         virtual bool childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const;
00056         virtual unsigned int limit() const;
00057 private:
00058         const BSGS<PERM, TRANS> &m_G;
00059         const BSGS<PERM, TRANS> &m_H;
00060 };
00061 
00062 //
00063 //     ----       IMPLEMENTATION
00064 //
00065 
00066 template <class PERM, class TRANS>
00067 GroupIntersectionPredicate<PERM,TRANS>::GroupIntersectionPredicate(const BSGS<PERM, TRANS> &g, const BSGS<PERM, TRANS> &h) 
00068         : m_G(g), m_H(h) 
00069 {
00070         BOOST_ASSERT(m_G.n == m_H.n);
00071     BOOST_ASSERT(m_G.order() <= m_H.order());
00072 }
00073 
00074 template <class PERM, class TRANS>
00075 bool GroupIntersectionPredicate<PERM,TRANS>::operator()(const PERM &p) const {
00076         return m_G.sifts(p) && m_H.sifts(p);
00077 }
00078 
00079 template <class PERM, class TRANS>
00080 bool GroupIntersectionPredicate<PERM,TRANS>::childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const {
00081         //TODO: check \beta_l^{g h^{-1}} \in \beta_l^{H_{(beta_1 ... beta_{l-1})}} instead
00082         //      cf. Handbook of Computational Group Theory, sec 4.6.6
00083         PERM siftee(m_H.n);
00084         const unsigned int m = m_H.sift(h, siftee, 0, i+1);
00085         return i+1 == m;
00086 }
00087 
00088 template <class PERM, class TRANS>
00089 unsigned int GroupIntersectionPredicate<PERM,TRANS>::limit() const { 
00090         return m_G.B.size(); 
00091 }
00092 
00093 }
00094 
00095 #endif // -- GROUPINTERSECTIONPREDICATE_H_