permlib 0.2.9
Library for permutation computations
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product_replacement_generator.h
1// ---------------------------------------------------------------------------
2//
3// This file is part of PermLib.
4//
5// Copyright (c) 2009-2011 Thomas Rehn <thomas@carmen76.de>
6// All rights reserved.
7//
8// Redistribution and use in source and binary forms, with or without
9// modification, are permitted provided that the following conditions
10// are met:
11// 1. Redistributions of source code must retain the above copyright
12// notice, this list of conditions and the following disclaimer.
13// 2. Redistributions in binary form must reproduce the above copyright
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15// documentation and/or other materials provided with the distribution.
16// 3. The name of the author may not be used to endorse or promote products
17// derived from this software without specific prior written permission.
18//
19// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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30// ---------------------------------------------------------------------------
31
32
33#ifndef PRODUCTREPLACEMENTGENERATOR_H
34#define PRODUCTREPLACEMENTGENERATOR_H
35
36#include <permlib/generator/random_generator.h>
37
38#include <vector>
39#include <boost/iterator/indirect_iterator.hpp>
40
41namespace permlib {
42
44template <class PERM>
46public:
48
52 template <class InputIterator>
53 ProductReplacementGenerator(const unsigned int n, InputIterator generatorsBegin, InputIterator generatorsEnd);
54
55 virtual PERM next();
56private:
57 std::vector<PERM> m_generators;
58 const unsigned int m_n;
59};
60
61//
62// ---- IMPLEMENTATION
63//
64
65template <class PERM>
66template <class InputIterator>
67ProductReplacementGenerator<PERM>::ProductReplacementGenerator(const unsigned int n, InputIterator generatorsBegin, InputIterator generatorsEnd)
68 : m_generators(boost::indirect_iterator<InputIterator, PERM>(generatorsBegin),
69 boost::indirect_iterator<InputIterator, PERM>(generatorsEnd)),
70 m_n(n)
71{
72 const unsigned int additionalElements = 10;
73 const unsigned int oldSize = m_generators.size();
74 const unsigned int replacementRounds = std::max(oldSize * 10, static_cast<unsigned int>(100));
75 if (oldSize == 0)
76 return;
77
78 m_generators.reserve(oldSize + additionalElements + 1);
79 for (unsigned int i = 0; i < additionalElements; ++i) {
80 m_generators.push_back(m_generators[randomInt(oldSize)]);
81 }
82 m_generators.push_back(PERM(m_generators[0].size()));
83
84 for (unsigned int k = 0; k < replacementRounds; ++k) {
85 next();
86 }
87}
88
89template <class PERM>
91 if (m_generators.size() == 0) {
92 return PERM(m_n);
93 }
94
95 unsigned int i = randomInt(m_generators.size() - 1);
96 unsigned int j = randomInt(m_generators.size() - 2);
97 if (j >= i) ++j;
98 switch (randomInt(4)) {
99 case 0:
100 m_generators[i] *= m_generators[j]; break;
101 case 1:
102 m_generators[i] *= ~m_generators[j]; break;
103 case 2:
104 m_generators[i] ^= m_generators[j]; break;
105 case 3:
106 m_generators[i] ^= ~m_generators[j]; break;
107 }
108 m_generators[m_generators.size()-1] *= m_generators[i];
109 return m_generators[m_generators.size()-1];
110}
111
112}
113
114#endif // -- PRODUCTREPLACEMENTGENERATOR_H
virtual PERM next()
generates an element
Definition product_replacement_generator.h:90
ProductReplacementGenerator(const unsigned int n, InputIterator generatorsBegin, InputIterator generatorsEnd)
initializes class with group generators
Definition product_replacement_generator.h:67
abstract base class for random group element generators
Definition random_generator.h:42