product_replacement_generator.h

// ---------------------------------------------------------------------------
//
//  This file is part of PermLib.
//
// Copyright (c) 2009-2011 Thomas Rehn <thomas@carmen76.de>
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
// 3. The name of the author may not be used to endorse or promote products
//    derived from this software without specific prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
// OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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//
// ---------------------------------------------------------------------------
 
 
#ifndef PRODUCTREPLACEMENTGENERATOR_H
#define PRODUCTREPLACEMENTGENERATOR_H
 
#include <permlib/generator/random_generator.h>
 
#include <vector>
#include <boost/iterator/indirect_iterator.hpp>
 
namespace permlib {

template <class PERM>
class ProductReplacementGenerator : public RandomGenerator<PERM> {
public:

        template <class InputIterator>
        ProductReplacementGenerator(const unsigned int n, InputIterator generatorsBegin, InputIterator generatorsEnd);
        
        virtual PERM next();
private:
        std::vector<PERM> m_generators;
        const unsigned int m_n;
};
 
//
//     ----       IMPLEMENTATION
//
 
template <class PERM>
template <class InputIterator>
ProductReplacementGenerator<PERM>::ProductReplacementGenerator(const unsigned int n, InputIterator generatorsBegin, InputIterator generatorsEnd) 
        : m_generators(boost::indirect_iterator<InputIterator, PERM>(generatorsBegin), 
                                   boost::indirect_iterator<InputIterator, PERM>(generatorsEnd)),
                m_n(n)
{
        const unsigned int additionalElements = 10;
        const unsigned int oldSize = m_generators.size();
        const unsigned int replacementRounds = std::max(oldSize * 10, static_cast<unsigned int>(100));
        if (oldSize == 0)
                return;
        
        m_generators.reserve(oldSize + additionalElements + 1);
        for (unsigned int i = 0; i < additionalElements; ++i) {
                m_generators.push_back(m_generators[randomInt(oldSize)]);
        }
        m_generators.push_back(PERM(m_generators[0].size()));
        
        for (unsigned int k = 0; k < replacementRounds; ++k) {
                next();
        }
}
 
template <class PERM>
PERM ProductReplacementGenerator<PERM>::next() {
        if (m_generators.size() == 0) {
                return PERM(m_n);
        }
        
        unsigned int i = randomInt(m_generators.size() - 1);
        unsigned int j = randomInt(m_generators.size() - 2);
        if (j >= i) ++j;
        switch (randomInt(4)) {
        case 0:
                m_generators[i] *=  m_generators[j]; break;
        case 1:
                m_generators[i] *= ~m_generators[j]; break;
        case 2:
                m_generators[i] ^=  m_generators[j]; break;
        case 3:
                m_generators[i] ^= ~m_generators[j]; break;
        }
        m_generators[m_generators.size()-1] *= m_generators[i];
        return m_generators[m_generators.size()-1];
}
 
}
 
#endif // -- PRODUCTREPLACEMENTGENERATOR_H