schreier_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,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// ---------------------------------------------------------------------------
 
 
#ifndef SCHREIERGENERATOR_H_
#define SCHREIERGENERATOR_H_
 
#include <permlib/common.h>
#include <permlib/generator/generator.h>
 
#include <stack>
#include <boost/scoped_ptr.hpp>
#include <boost/tuple/tuple.hpp>
#include <boost/next_prior.hpp>
 
namespace permlib {


template <class PERM, class TRANS>
class SchreierGenerator : public Generator<PERM> {
public:
        typedef typename std::list<typename PERM::ptr>::const_iterator PERMlistIt;
        typedef typename std::list<unsigned long>::const_iterator TRANSlistIt;
        

        SchreierGenerator(const TRANS *U, PERMlistIt S_begin, PERMlistIt S_end);
        virtual ~SchreierGenerator();
 
        PERM next();
        bool hasNext();
        

        void update(TRANS *U, PERMlistIt S_begin, PERMlistIt S_end);
        

        void update(unsigned int j);
private:
        PERMlistIt m_Sbegin;
        PERMlistIt m_Scurrent;
        PERMlistIt m_Send;
        const TRANS *m_U;
        TRANSlistIt m_Ubegin;
        TRANSlistIt m_Ucurrent;
        TRANSlistIt m_Uend;
        unsigned int m_posS;
        unsigned int m_posSlimit;
        unsigned int m_posU;
        unsigned int m_posUlimit;
 
        PERM* m_u_beta;
        unsigned long m_beta;
 
        std::stack<boost::tuple<unsigned int, unsigned int, unsigned int, unsigned int> > m_stackTodo;

        bool advance();
        void init();
        void reset();
};
 
//
//     ----       IMPLEMENTATION
//
 
template <class PERM, class TRANS>
SchreierGenerator<PERM, TRANS>::SchreierGenerator(const TRANS *U, PERMlistIt S_begin, PERMlistIt S_end)
                : m_Sbegin(S_begin), m_Scurrent(S_begin), m_Send(S_end),
                  m_U(U), m_Ubegin(m_U->begin()), m_Ucurrent(m_U->begin()), m_Uend(m_U->end()),
                  m_posS(0), m_posSlimit(0), m_posU(0), m_posUlimit(0), m_u_beta(0)
{
        init();
}
 
template <class PERM, class TRANS>
SchreierGenerator<PERM, TRANS>::~SchreierGenerator() {
        delete m_u_beta;
}
 
template <class PERM, class TRANS>
void SchreierGenerator<PERM, TRANS>::init() {
        m_beta = *m_Ucurrent;
        delete m_u_beta;
        m_u_beta = m_U->at(m_beta);
}
 
 
template <class PERM, class TRANS>
bool SchreierGenerator<PERM, TRANS>::hasNext() {
        if (m_Send != m_Scurrent && m_Uend != m_Ucurrent && (!m_posUlimit || m_posU < m_posUlimit)) {
                const PERM &x = **m_Scurrent;
                if (m_U->trivialByDefinition(x, x / m_beta)) {
                        advance();
                        return hasNext();
                }
                return true;
        }
 
        if (!m_stackTodo.empty()) {
                boost::tuple<unsigned int, unsigned int, unsigned int, unsigned int> lastTuple = m_stackTodo.top();
                m_stackTodo.pop();
 
                m_posS = boost::get<0>(lastTuple);
                m_posSlimit = boost::get<1>(lastTuple);
                m_posU = boost::get<2>(lastTuple);
                m_posUlimit = boost::get<3>(lastTuple);
                reset();
 
                return hasNext();
        }
        return false;
}
 
template <class PERM, class TRANS>
bool SchreierGenerator<PERM, TRANS>::advance() {
        ++m_Scurrent;
        ++m_posS;
        if (m_Scurrent == m_Send) {
                m_Scurrent = boost::next(m_Sbegin, m_posSlimit);
                m_posS = m_posSlimit;
                ++m_Ucurrent;
                ++m_posU;
                if (m_Ucurrent != m_Uend)
                        init();
                else
                        return false;
        }
        return true;
}
 
template <class PERM, class TRANS>
PERM SchreierGenerator<PERM, TRANS>::next() {
        BOOST_ASSERT(m_Scurrent != m_Send);
        BOOST_ASSERT(m_Ucurrent != m_Uend);
 
        PERMLIB_DEBUG(std::cout << "s = " << m_posS << "; u = " << m_posU << std::endl;)
        const PERM &x = **m_Scurrent;
 
        PERM g = *m_u_beta * x;
        boost::scoped_ptr<PERM> u_beta_ptr2(m_U->at(x / m_beta));
        u_beta_ptr2->invertInplace();
        g *= *u_beta_ptr2;
 
        advance();
 
        return g;
}
 
template <class PERM, class TRANS>
void SchreierGenerator<PERM, TRANS>::reset() {
        m_Scurrent = m_Sbegin;
        m_Ucurrent = m_Ubegin;
        int i = m_posS;
        while (--i>=0) ++m_Scurrent;
        i = m_posU;
        while (--i>=0) ++m_Ucurrent;
 
        if (m_Ucurrent != m_Uend)
                init();
}
 
template <class PERM, class TRANS>
void SchreierGenerator<PERM, TRANS>:: update(TRANS *U, PERMlistIt S_begin, PERMlistIt S_end) {
        if (U == m_U && S_begin == m_Sbegin && S_end == m_Send)
                return;
        m_U = U;
        m_Sbegin = S_begin;
        m_Send = S_end;
        m_Ubegin = U->begin();
        m_Uend = U->end();
        reset();
}
 
template <class PERM, class TRANS>
void SchreierGenerator<PERM, TRANS>:: update(unsigned int j) {
        m_stackTodo.push(boost::make_tuple(m_posS, m_posSlimit, m_posU, m_posUlimit));
        m_posUlimit = m_posU;
        m_posS = j;
        m_posSlimit = j;
        m_posU = 0;
        reset();
}
 
}
 
#endif // -- SCHREIERGENERATOR_H_