permlib 0.2.9
Library for permutation computations
lex_smaller_image_predicate.h
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31
32
33#ifndef LEXSMALLERIMAGE_PREDICATE_H_
34#define LEXSMALLERIMAGE_PREDICATE_H_
35
36#include <permlib/predicate/subgroup_predicate.h>
37
38#include <set>
39#include <boost/foreach.hpp>
40#include <boost/dynamic_bitset.hpp>
41
42namespace permlib {
43
45
48template <class PERM>
50public:
52
59 template<class ForwardIterator>
60 LexSmallerImagePredicate(unsigned int n, ForwardIterator zerosBegin, ForwardIterator zerosEnd, ForwardIterator onesBegin, ForwardIterator onesEnd);
61
62 virtual bool operator()(const PERM &p) const;
63 virtual bool childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const;
64 virtual unsigned int limit() const;
65private:
66 boost::dynamic_bitset<> m_zeros;
67 boost::dynamic_bitset<> m_ones;
68 unsigned long m_fixed;
69};
70
71//
72// ---- IMPLEMENTATION
73//
74
75template <class PERM>
76template<class ForwardIterator>
77LexSmallerImagePredicate<PERM>::LexSmallerImagePredicate(unsigned int n, ForwardIterator zerosBegin, ForwardIterator zerosEnd, ForwardIterator onesBegin, ForwardIterator onesEnd)
78 : m_zeros(n), m_ones(n), m_fixed(0)
79{
80 while (zerosBegin != zerosEnd) {
81 m_zeros.set(*zerosBegin++, 1);
82 ++m_fixed;
83 }
84 while (onesBegin != onesEnd) {
85 m_ones.set(*onesBegin++, 1);
86 ++m_fixed;
87 }
88}
89
90
91template <class PERM>
93 for (unsigned int i = 0; i < p.size(); ++i) {
94 const dom_int pi = p / i;
95 if (pi == i)
96 continue;
97 if (m_ones[i] && m_zeros[pi]) {
98 PERMLIB_DEBUG( std::cout << i << " , " << pi << " !0 -> 0 TRUE" << std::endl; )
99 return true;
100 }
101 if (m_zeros[i] && !m_zeros[pi]) {
102 PERMLIB_DEBUG( std::cout << i << " , " << pi << " 0 -> !0 FALSE" << std::endl; )
103 return false;
104 }
105 }
106 return false;
107}
108
109template <class PERM>
110bool LexSmallerImagePredicate<PERM>::childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const {
111 // Because limit() does not depend on h, we have to check at every node
112 // whether we have already found a element, which maps the given sets to a
113 // lexicographically smaller set
114 if ((*this)(h)) {
115 PERMLIB_DEBUG( std::cout << h << " is already the desired element; TRUE" << std::endl; )
116 return true;
117 }
118 if (m_zeros[beta_i] && !m_zeros[h / beta_i]) {
119 PERMLIB_DEBUG( std::cout << (h / beta_i) << " mapping zero " << beta_i << " to non-zero; FALSE" << std::endl; )
120 return false;
121 }
122 return true;
123}
124
125template <class PERM>
127 return m_fixed;
128}
129
130}
131
132#endif // -- LEXSMALLERIMAGE_PREDICATE_H_
coset-type predicate for group elements that map one set of zeros and ones to a lex-smaller set (w....
Definition: lex_smaller_image_predicate.h:49
virtual bool operator()(const PERM &p) const
true iff group element fulfills predicate
Definition: lex_smaller_image_predicate.h:92
virtual unsigned int limit() const
limit of recursion depth in backtrack search
Definition: lex_smaller_image_predicate.h:126
LexSmallerImagePredicate(unsigned int n, ForwardIterator zerosBegin, ForwardIterator zerosEnd, ForwardIterator onesBegin, ForwardIterator onesEnd)
constructor
Definition: lex_smaller_image_predicate.h:77
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: lex_smaller_image_predicate.h:110
abstract base class for subgroup (and coset) predicates
Definition: subgroup_predicate.h:45