bsgs_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 BSGSGENERATOR_H_
#define BSGSGENERATOR_H_
 
#include <permlib/common.h>
#include <permlib/generator/generator.h>
 
#include <boost/scoped_ptr.hpp>
 
namespace permlib {


template <class TRANS>
class BSGSGenerator : public Generator<typename TRANS::PERMtype> {
private:
        typedef typename TRANS::PERMtype PERM;
public:

        BSGSGenerator(const std::vector<TRANS>& U);
        virtual ~BSGSGenerator() {}
        
        virtual PERM next();
        virtual bool hasNext();
private:
        const std::vector<TRANS>& m_U;
        std::vector<std::list<unsigned long>::const_iterator > m_Upositions;
        bool m_hasNext;
};
 
//
//     ----       IMPLEMENTATION
//
 
template <class TRANS>
BSGSGenerator<TRANS>::BSGSGenerator(const std::vector<TRANS>& U)
                : m_U(U), m_Upositions(U.size()), m_hasNext(true)
{ 
        for (unsigned int i = 0; i < m_U.size(); ++i) {
                m_Upositions[i] = m_U[i].begin();
        }
}
 
 
template <class TRANS>
bool BSGSGenerator<TRANS>::hasNext() {
        return m_hasNext;
}
 
 
template <class TRANS>
typename BSGSGenerator<TRANS>::PERM BSGSGenerator<TRANS>::next() {
        BOOST_ASSERT( m_hasNext );
        PERM g(m_U[0].n());
        for (int i = m_Upositions.size() - 1; i >= 0; --i) {
                boost::scoped_ptr<PERM> u_beta( m_U[i].at( *m_Upositions[i] ) );
                BOOST_ASSERT( u_beta );
                g *= *u_beta;
        }
        
        // advance position
        int i;
        for (i = m_Upositions.size() - 1; i >= 0; --i) {
                m_Upositions[i]++;
                if (m_Upositions[i] == m_U[i].end())
                        m_Upositions[i] = m_U[i].begin();
                else
                        break;
        }
        if ( i < 0 )
                m_hasNext = false;
        
        return g;
}
 
}
 
#endif // -- BSGSGENERATOR_H_