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/********************* */
/*! \file dual_simplex.h
** \verbatim
** Top contributors (to current version):
** Tim King, Mathias Preiner, Morgan Deters
** This file is part of the CVC4 project.
** Copyright (c) 2009-2021 by the authors listed in the file AUTHORS
** in the top-level source directory and their institutional affiliations.
** All rights reserved. See the file COPYING in the top-level source
** directory for licensing information.\endverbatim
**
** \brief This is an implementation of the Simplex Module for the Simplex for
** DPLL(T) decision procedure.
**
** This implements the Simplex module for the Simpelx for DPLL(T) decision
** procedure.
** See the Simplex for DPLL(T) technical report for more background.(citation?)
** This shares with the theory a Tableau, and a PartialModel that:
** - satisfies the equalities in the Tableau, and
** - the assignment for the non-basic variables satisfies their bounds.
** This is required to either produce a conflict or satisifying PartialModel.
** Further, we require being told when a basic variable updates its value.
**
** During the Simplex search we maintain a queue of variables.
** The queue is required to contain all of the basic variables that voilate
** their bounds.
** As elimination from the queue is more efficient to be done lazily,
** we do not maintain that the queue of variables needs to be only basic
** variables or only variables that satisfy their bounds.
**
** The simplex procedure roughly follows Alberto's thesis. (citation?)
** There is one round of selecting using a heuristic pivoting rule.
** (See PreferenceFunction Documentation for the available options.)
** The non-basic variable is the one that appears in the fewest pivots.
** (Bruno says that Leonardo invented this first.)
** After this, Bland's pivot rule is invoked.
**
** During this proccess, we periodically inspect the queue of variables to
** 1) remove now extraneous extries,
** 2) detect conflicts that are "waiting" on the queue but may not be detected
** by the current queue heuristics, and
** 3) detect multiple conflicts.
**
** Conflicts are greedily slackened to use the weakest bounds that still
** produce the conflict.
**
** Extra things tracked atm: (Subject to change at Tim's whims)
** - A superset of all of the newly pivoted variables.
** - A queue of additional conflicts that were discovered by Simplex.
** These are theory valid and are currently turned into lemmas
**/
#include "cvc4_private.h"
#pragma once
#include "theory/arith/simplex.h"
#include "util/statistics_registry.h"
namespace CVC4 {
namespace theory {
namespace arith {
class DualSimplexDecisionProcedure : public SimplexDecisionProcedure{
public:
DualSimplexDecisionProcedure(LinearEqualityModule& linEq, ErrorSet& errors, RaiseConflict conflictChannel, TempVarMalloc tvmalloc);
Result::Sat findModel(bool exactResult) override
{
return dualFindModel(exactResult);
}
private:
/**
* Maps a variable to how many times they have been used as a pivot in the
* simplex search.
*/
DenseMultiset d_pivotsInRound;
Result::Sat dualFindModel(bool exactResult);
/**
* This is the main simplex for DPLL(T) loop.
* It runs for at most maxIterations.
*
* Returns true iff it has found a conflict.
* d_conflictVariable will be set and the conflict for this row is reported.
*/
bool searchForFeasibleSolution(uint32_t maxIterations);
bool processSignals(){
TimerStat &timer = d_statistics.d_processSignalsTime;
IntStat& conflictStat = d_statistics.d_recentViolationCatches;
return standardProcessSignals(timer, conflictStat);
}
/** These fields are designed to be accessible to TheoryArith methods. */
class Statistics {
public:
IntStat d_statUpdateConflicts;
TimerStat d_processSignalsTime;
IntStat d_simplexConflicts;
IntStat d_recentViolationCatches;
TimerStat d_searchTime;
ReferenceStat<uint32_t> d_finalCheckPivotCounter;
Statistics(uint32_t& pivots);
~Statistics();
} d_statistics;
};/* class DualSimplexDecisionProcedure */
}/* CVC4::theory::arith namespace */
}/* CVC4::theory namespace */
}/* CVC4 namespace */
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