lex_smaller_image_predicate.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
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// ---------------------------------------------------------------------------
 
 
#ifndef LEXSMALLERIMAGE_PREDICATE_H_
#define LEXSMALLERIMAGE_PREDICATE_H_
 
#include <permlib/predicate/subgroup_predicate.h>
 
#include <set>
#include <boost/foreach.hpp>
#include <boost/dynamic_bitset.hpp>
 
namespace permlib {


template <class PERM>
class LexSmallerImagePredicate : public SubgroupPredicate<PERM> {
public:

        template<class ForwardIterator>
        LexSmallerImagePredicate(unsigned int n, ForwardIterator zerosBegin, ForwardIterator zerosEnd, ForwardIterator onesBegin, ForwardIterator onesEnd);
 
        virtual bool operator()(const PERM &p) const;
        virtual bool childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const;
        virtual unsigned int limit() const;
private:
        boost::dynamic_bitset<> m_zeros;
        boost::dynamic_bitset<> m_ones;
        unsigned long m_fixed;
};
 
//
//     ----       IMPLEMENTATION
//
 
template <class PERM>
template<class ForwardIterator>
LexSmallerImagePredicate<PERM>::LexSmallerImagePredicate(unsigned int n, ForwardIterator zerosBegin, ForwardIterator zerosEnd, ForwardIterator onesBegin, ForwardIterator onesEnd)
        : m_zeros(n), m_ones(n), m_fixed(0)
{ 
        while (zerosBegin != zerosEnd) {
                m_zeros.set(*zerosBegin++, 1);
                ++m_fixed;
        }
        while (onesBegin != onesEnd) {
                m_ones.set(*onesBegin++, 1);
                ++m_fixed;
        }
}
 
 
template <class PERM>
bool LexSmallerImagePredicate<PERM>::operator()(const PERM &p) const {
        for (unsigned int i = 0; i < p.size(); ++i) {
                const dom_int pi = p / i;
                if (pi == i)
                        continue;
                if (m_ones[i] && m_zeros[pi]) {
                        PERMLIB_DEBUG( std::cout << i << " , " << pi << "  !0 ->  0  TRUE" << std::endl; )
                        return true;
                }
                if (m_zeros[i] && !m_zeros[pi]) {
                        PERMLIB_DEBUG( std::cout << i << " , " << pi << "  0  -> !0  FALSE" << std::endl; )
                        return false;
                }
        }
        return false;
}
 
template <class PERM>
bool LexSmallerImagePredicate<PERM>::childRestriction(const PERM &h, unsigned int i, unsigned long beta_i) const {
        // Because limit() does not depend on h, we have to check at every node
        // whether we have already found a element, which maps the given sets to a
        // lexicographically smaller set
        if ((*this)(h)) {
                PERMLIB_DEBUG( std::cout << h << " is already the desired element; TRUE" << std::endl; )
                return true;
        }
        if (m_zeros[beta_i] && !m_zeros[h / beta_i]) {
                PERMLIB_DEBUG( std::cout << (h / beta_i) << " mapping zero " << beta_i << " to non-zero; FALSE" << std::endl; )
                return false;
        }
        return true;
}
 
template <class PERM>
unsigned int LexSmallerImagePredicate<PERM>::limit() const {
        return m_fixed;
}
 
}
 
#endif // -- LEXSMALLERIMAGE_PREDICATE_H_