permlib  0.2.9
Library for permutation computations
group_intersection_predicate.h
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31 
32 
33 #ifndef GROUPINTERSECTIONPREDICATE_H_
34 #define GROUPINTERSECTIONPREDICATE_H_
35 
36 #include <permlib/bsgs.h>
37 #include <permlib/predicate/subgroup_predicate.h>
38 
39 #include <boost/foreach.hpp>
40 
41 namespace permlib {
42 
44 template <class PERM, class TRANS>
46 public:
48 
53 
54  virtual bool operator()(const PERM &p) const;
55  virtual bool childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const;
56  virtual unsigned int limit() const;
57 private:
58  const BSGS<PERM, TRANS> &m_G;
59  const BSGS<PERM, TRANS> &m_H;
60 };
61 
62 //
63 // ---- IMPLEMENTATION
64 //
65 
66 template <class PERM, class TRANS>
68  : m_G(g), m_H(h)
69 {
70  BOOST_ASSERT(m_G.n == m_H.n);
71  BOOST_ASSERT(m_G.order() <= m_H.order());
72 }
73 
74 template <class PERM, class TRANS>
76  return m_G.sifts(p) && m_H.sifts(p);
77 }
78 
79 template <class PERM, class TRANS>
80 bool GroupIntersectionPredicate<PERM,TRANS>::childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const {
81  //TODO: check \beta_l^{g h^{-1}} \in \beta_l^{H_{(beta_1 ... beta_{l-1})}} instead
82  // cf. Handbook of Computational Group Theory, sec 4.6.6
83  PERM siftee(m_H.n);
84  const unsigned int m = m_H.sift(h, siftee, 0, i+1);
85  return i+1 == m;
86 }
87 
88 template <class PERM, class TRANS>
90  return m_G.B.size();
91 }
92 
93 }
94 
95 #endif // -- GROUPINTERSECTIONPREDICATE_H_
predicate for the subgroup that arises as the intersection of two given groups
Definition: group_intersection_predicate.h:45
virtual bool childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const
checks if a given group element should not be followed in backtrack search
Definition: group_intersection_predicate.h:80
virtual bool operator()(const PERM &p) const
true iff group element fulfills predicate
Definition: group_intersection_predicate.h:75
abstract base class for subgroup (and coset) predicates
Definition: subgroup_predicate.h:45
Represents a base and strong generating set (BSGS)
Definition: bsgs.h:58
virtual unsigned int limit() const
limit of recursion depth in backtrack search
Definition: group_intersection_predicate.h:89
GroupIntersectionPredicate(const BSGS< PERM, TRANS > &g, const BSGS< PERM, TRANS > &h)
constructor
Definition: group_intersection_predicate.h:67
Definition: abstract_bsgs.h:49