MsmSlice.h

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/* Frobby: Software for monomial ideal computations.
   Copyright (C) 2007 Bjarke Hammersholt Roune (www.broune.com)
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
 
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see http://www.gnu.org/licenses/.
*/
#ifndef MSM_SLICE_GUARD
#define MSM_SLICE_GUARD
 
#include "Slice.h"
#include "Term.h"
#include "Ideal.h"
 
class TermConsumer;
class Projection;
class MsmStrategy;
 
class MsmSlice : public Slice {
 public:
  MsmSlice(MsmStrategy& strategy);
  MsmSlice(MsmStrategy& strategy,
           const Ideal& ideal,
           const Ideal& subtract,
           const Term& multiply,
           TermConsumer* consumer);
 
  TermConsumer* getConsumer() {return _consumer;}
 
  // *** Mutators
 
  // A base case is reached if not all variables divide the lcm of
  // getIdeal(), or if getGeneratorCount() is 2, or if getIdeal() is
  // square free.
  virtual bool baseCase(bool simplified);
 
  virtual Slice& operator=(const Slice& slice);
 
  virtual bool simplifyStep();
 
  void setToProjOf(const MsmSlice& slice,
                   const Projection& projection,
                   TermConsumer* consumer);
 
  // Efficiently swaps the values of *this and slice.
  void swap(MsmSlice& slice);
 
  virtual bool innerSlice(const Term& pivot);
  virtual void outerSlice(const Term& pivot);
 
 private:
  // Removes those generators g of getIdeal() such that g[i] equals
  // getLcm()[i] for two distinct i. This is done iteratively until no
  // more generators can be removed in this way. Returns true if any
  // generators were removed.
  bool removeDoubleLcm();
 
  // Calculates the gcd of those generators of getIdeal() that are
  // divisible by var. This gcd is then divided by var to yield a
  // lower bound on the content of the slice. Returns false if a base
  // case is detected. The real functionality is slight more
  // sophisticated.
  virtual bool getLowerBound(Term& bound, size_t var) const;
 
  // Outputs the content of the slice to consumer. It is a
  // precondition that the slice is fully simplified and that
  // getVarCount() returns 2.
  void twoVarBaseCase();
 
  // Outputs the content of the slice to consumer. It is a
  // precondition that the slice is fully simplified and that
  // getVarCount() plus one equals
  // getIdeal().getGeneratorCount(). This will, due to simplification,
  // be true if there is exactly one generator that is nowhere equal
  // to the lcm of getIdeal().
  void oneMoreGeneratorBaseCase();
 
  // Outputs the content of the slice to consumer or returns false. It
  // is a precondition that the slice is fully simplified. Returns
  // true if there are exactly two generators that are nowhere equal
  // to the lcm of getIdeal().
  bool twoNonMaxBaseCase();
 
  TermConsumer* _consumer;
};
 
inline void swap(MsmSlice& a, MsmSlice& b) { a.swap(b); }
 
 
#endif