base_transpose.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
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// 1. Redistributions of source code must retain the above copyright
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//    notice, this list of conditions and the following disclaimer in the
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//    derived from this software without specific prior written permission.
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// ---------------------------------------------------------------------------
 
 
#ifndef BASETRANSPOSE_H_
#define BASETRANSPOSE_H_
 
#include <permlib/predicate/pointwise_stabilizer_predicate.h>
#include <permlib/generator/generator.h>
 
#include <boost/scoped_ptr.hpp>
#include <boost/iterator/indirect_iterator.hpp>
#include <boost/next_prior.hpp>
 
namespace permlib {


template<class PERM, class TRANS>
class BaseTranspose {
public:
    BaseTranspose();
    virtual ~BaseTranspose() {}


    void transpose(BSGS<PERM,TRANS> &bsgs, unsigned int i) const;

    mutable unsigned int m_statScheierGeneratorsConsidered;
    mutable unsigned int m_statNewGenerators;
protected:
        typedef std::list<typename PERM::ptr> PERMlist;
        

    virtual Generator<PERM>* setupGenerator(BSGS<PERM,TRANS> &bsgs, unsigned int i, const PERMlist &S_i, const TRANS &U_i) const = 0;
};
 
//
//     ----       IMPLEMENTATION
//
 
template<class PERM, class TRANS>
BaseTranspose<PERM,TRANS>::BaseTranspose() 
        : m_statScheierGeneratorsConsidered(0), m_statNewGenerators(0)
{ }
 
template<class PERM, class TRANS>
void BaseTranspose<PERM,TRANS>::transpose(BSGS<PERM,TRANS> &bsgs, unsigned int i) const {
        std::vector<dom_int> &B = bsgs.B;
        std::vector<TRANS> &U = bsgs.U;
 
        if (i+1 >= B.size())
                // illegal transpose index
                return;
 
        PERMlist S_i;
        std::copy_if(bsgs.S.begin(), bsgs.S.end(), std::back_inserter(S_i), PointwiseStabilizerPredicate<PERM>(B.begin(), B.begin() + i));
 
        std::swap(B[i], B[i+1]);
 
        PERMlist S_i1;
        std::copy_if(bsgs.S.begin(), bsgs.S.end(), std::back_inserter(S_i1), PointwiseStabilizerPredicate<PERM>(B.begin(), B.begin() + (i+1)));
 
        unsigned int targetTransversalSize = U[i+1].size() * U[i].size();
 
        // new transversal
        TRANS U_i(U[i].n());
        U_i.orbit(B[i], S_i);
        targetTransversalSize /= U_i.size();
 
        m_statScheierGeneratorsConsidered = 0;
        m_statNewGenerators = 0;
        TRANS U_i1(U[i+1].n());
        U_i1.orbit(B[i+1], S_i1);
    boost::scoped_ptr<Generator<PERM> > generator(setupGenerator(bsgs, i, S_i, U_i));
    BOOST_ASSERT(generator != 0);
    
        while (U_i1.size() < targetTransversalSize) {
                bool newGeneratorFound = false;
                while (generator->hasNext()) {
                        PERM g = generator->next();
                        ++m_statScheierGeneratorsConsidered;
                        boost::indirect_iterator<typename PERMlist::iterator> sBegin(S_i1.begin()), sEnd(S_i1.end());
                        if (!U_i1.contains(g / B[i+1]) && std::find(sBegin, sEnd, g) == sEnd) {
                                g.flush();
                                boost::shared_ptr<PERM> gen(new PERM(g));
                                S_i1.push_front(gen);
                                ++m_statNewGenerators;
                                U_i1.orbitUpdate(B[i+1], S_i1, gen);
                                newGeneratorFound = true;
                                break;
                        }
                }
                if (!newGeneratorFound)
                        // we have exhausted all available generators, and we won't find any new ones in the loop
                        break;
        }
        BOOST_ASSERT(U_i1.size() >= targetTransversalSize);
 
        bsgs.S.insert(bsgs.S.end(), S_i1.begin(), boost::next(S_i1.begin(), m_statNewGenerators));
        U[i] = U_i;
        U[i+1] = U_i1;
}
 
}
 
#endif // -- BASETRANSPOSE_H_