permlib  0.2.9
Library for permutation computations
bsgs_generator.h
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31 
32 
33 #ifndef BSGSGENERATOR_H_
34 #define BSGSGENERATOR_H_
35 
36 #include <permlib/common.h>
37 #include <permlib/generator/generator.h>
38 
39 #include <boost/scoped_ptr.hpp>
40 
41 namespace permlib {
42 
44 
47 template <class TRANS>
48 class BSGSGenerator : public Generator<typename TRANS::PERMtype> {
49 private:
50  typedef typename TRANS::PERMtype PERM;
51 public:
53 
56  BSGSGenerator(const std::vector<TRANS>& U);
57  virtual ~BSGSGenerator() {}
58 
59  virtual PERM next();
60  virtual bool hasNext();
61 private:
62  const std::vector<TRANS>& m_U;
63  std::vector<std::list<unsigned long>::const_iterator > m_Upositions;
64  bool m_hasNext;
65 };
66 
67 //
68 // ---- IMPLEMENTATION
69 //
70 
71 template <class TRANS>
72 BSGSGenerator<TRANS>::BSGSGenerator(const std::vector<TRANS>& U)
73  : m_U(U), m_Upositions(U.size()), m_hasNext(true)
74 {
75  for (unsigned int i = 0; i < m_U.size(); ++i) {
76  m_Upositions[i] = m_U[i].begin();
77  }
78 }
79 
80 
81 template <class TRANS>
83  return m_hasNext;
84 }
85 
86 
87 template <class TRANS>
88 typename BSGSGenerator<TRANS>::PERM BSGSGenerator<TRANS>::next() {
89  BOOST_ASSERT( m_hasNext );
90  PERM g(m_U[0].n());
91  for (int i = m_Upositions.size() - 1; i >= 0; --i) {
92  boost::scoped_ptr<PERM> u_beta( m_U[i].at( *m_Upositions[i] ) );
93  BOOST_ASSERT( u_beta );
94  g *= *u_beta;
95  }
96 
97  // advance position
98  int i;
99  for (i = m_Upositions.size() - 1; i >= 0; --i) {
100  m_Upositions[i]++;
101  if (m_Upositions[i] == m_U[i].end())
102  m_Upositions[i] = m_U[i].begin();
103  else
104  break;
105  }
106  if ( i < 0 )
107  m_hasNext = false;
108 
109  return g;
110 }
111 
112 }
113 
114 #endif // -- BSGSGENERATOR_H_
BSGSGenerator(const std::vector< TRANS > &U)
constructor
Definition: bsgs_generator.h:72
virtual PERM next()
generates an element
Definition: bsgs_generator.h:88
interface for group element generators
Definition: generator.h:40
virtual bool hasNext()
true, iff more elements can be generated
Definition: bsgs_generator.h:82
stateful generator of BSGS elements
Definition: bsgs_generator.h:48
Definition: abstract_bsgs.h:49