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+/*********************                                                        */
+/*! \file simplex.h
+ ** \verbatim
+ ** Original author: taking
+ ** Major contributors: none
+ ** Minor contributors (to current version): kshitij, mdeters
+ ** This file is part of the CVC4 prototype.
+ ** Copyright (c) 2009-2012  New York University and The University of Iowa
+ ** 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/dense_map.h"
+#include "util/statistics_registry.h"
+#include <stdint.h>
+
+namespace CVC4 {
+namespace theory {
+namespace arith {
+
+class FCSimplexDecisionProcedure : public SimplexDecisionProcedure{
+public:
+  FCSimplexDecisionProcedure(LinearEqualityModule& linEq, ErrorSet& errors, RaiseConflict conflictChannel, TempVarMalloc tvmalloc);
+
+  Result::Sat findModel(bool exactResult);
+
+  // other error variables are dropping
+  WitnessImprovement dualLikeImproveError(ArithVar evar);
+  WitnessImprovement primalImproveError(ArithVar evar);
+
+  // dual like
+  // - found conflict
+  // - satisfied error set
+  Result::Sat dualLike();
+
+private:
+  static const uint32_t PENALTY = 4;
+  DenseMultiset d_scores;
+  void decreasePenalties(){ d_scores.removeOneOfEverything(); }
+  uint32_t penalty(ArithVar x) const { return d_scores.count(x); }
+  void setPenalty(ArithVar x, WitnessImprovement w){
+    if(improvement(w)){
+      if(d_scores.count(x) > 0){
+        d_scores.removeAll(x);
+      }
+    }else{
+      d_scores.setCount(x, PENALTY);
+    }
+  }
+
+  /** The size of the focus set. */
+  uint32_t d_focusSize;
+
+  /** The current error focus variable. */
+  ArithVar d_focusErrorVar;
+
+  /**
+   * The signs of the coefficients in the focus set.
+   * This is empty until this has been loaded.
+   */
+  DenseMap<const Rational*> d_focusCoefficients;
+
+  /**
+   * Loads the signs of the coefficients of the variables on the row d_focusErrorVar
+   * into d_focusSgns.
+   */
+  void loadFocusSigns();
+
+  /** Unloads the information from d_focusSgns. */
+  void unloadFocusSigns();
+
+  /**
+   * The signs of a variable in the row of d_focusErrorVar.
+   * d_focusSgns must be loaded.
+   */
+  const Rational& focusCoefficient(ArithVar nb) const;
+
+  int32_t d_pivotBudget;
+  // enum PivotImprovement {
+  //   ErrorDropped,
+  //   NonDegenerate,
+  //   HeuristicDegenerate,
+  //   BlandsDegenerate
+  // };
+
+  WitnessImprovement d_prevWitnessImprovement;
+  uint32_t d_witnessImprovementInARow;
+
+  uint32_t degeneratePivotsInARow() const;
+
+  static const uint32_t s_focusThreshold = 6;
+  static const uint32_t s_maxDegeneratePivotsBeforeBlandsOnLeaving = 100;
+  static const uint32_t s_maxDegeneratePivotsBeforeBlandsOnEntering = 10;
+
+  DenseMap<uint32_t> d_leavingCountSinceImprovement;
+  void increaseLeavingCount(ArithVar x){
+    if(!d_leavingCountSinceImprovement.isKey(x)){
+      d_leavingCountSinceImprovement.set(x,1);
+    }else{
+      (d_leavingCountSinceImprovement.get(x))++;
+    }
+  }
+  LinearEqualityModule::UpdatePreferenceFunction selectLeavingFunction(ArithVar x){
+    bool useBlands = d_leavingCountSinceImprovement.isKey(x) &&
+      d_leavingCountSinceImprovement[x] >= s_maxDegeneratePivotsBeforeBlandsOnEntering;
+    return useBlands ?
+      &LinearEqualityModule::preferWitness<false>:
+      &LinearEqualityModule::preferWitness<true>;
+  }
+
+  bool debugDualLike(WitnessImprovement w, std::ostream& out,
+                     int instance,
+                     uint32_t prevFocusSize, uint32_t prevErrorSize) const;
+
+  void debugPrintSignal(ArithVar updated) const;
+
+  ArithVarVec d_sgnDisagreements;
+
+  //static PivotImprovement pivotImprovement(const UpdateInfo& selected, bool useBlands = false);
+
+  void logPivot(WitnessImprovement w);
+
+  void updateAndSignal(const UpdateInfo& selected, WitnessImprovement w);
+
+  UpdateInfo selectPrimalUpdate(ArithVar error,
+                                LinearEqualityModule::UpdatePreferenceFunction upf,
+                                LinearEqualityModule::VarPreferenceFunction bpf);
+
+
+  UpdateInfo selectUpdateForDualLike(ArithVar basic){
+    TimerStat::CodeTimer codeTimer(d_statistics.d_selectUpdateForDualLike);
+
+    LinearEqualityModule::UpdatePreferenceFunction upf =
+      &LinearEqualityModule::preferWitness<true>;
+    LinearEqualityModule::VarPreferenceFunction bpf =
+      &LinearEqualityModule::minVarOrder;
+    return selectPrimalUpdate(basic, upf, bpf);
+  }
+
+  UpdateInfo selectUpdateForPrimal(ArithVar basic, bool useBlands){
+    TimerStat::CodeTimer codeTimer(d_statistics.d_selectUpdateForPrimal);
+
+    LinearEqualityModule::UpdatePreferenceFunction upf = useBlands ?
+      &LinearEqualityModule::preferWitness<false>:
+      &LinearEqualityModule::preferWitness<true>;
+
+    LinearEqualityModule::VarPreferenceFunction bpf = useBlands ?
+      &LinearEqualityModule::minVarOrder :
+      &LinearEqualityModule::minRowLength;
+    bpf = &LinearEqualityModule::minVarOrder;
+
+    return selectPrimalUpdate(basic, upf, bpf);
+  }
+  WitnessImprovement selectFocusImproving() ;
+
+  WitnessImprovement focusUsingSignDisagreements(ArithVar basic);
+  WitnessImprovement focusDownToLastHalf();
+  WitnessImprovement adjustFocusShrank(const ArithVarVec& drop);
+  WitnessImprovement focusDownToJust(ArithVar v);
+
+
+  void adjustFocusAndError(const UpdateInfo& up, const AVIntPairVec& focusChanges);
+
+  /**
+   * 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 initialProcessSignals(){
+    TimerStat &timer = d_statistics.d_initialSignalsTime;
+    IntStat& conflictStat  = d_statistics.d_initialConflicts;
+    bool res = standardProcessSignals(timer, conflictStat);
+    d_focusSize = d_errorSet.focusSize();
+    return res;
+  }
+
+  static bool debugCheckWitness(const UpdateInfo& inf, WitnessImprovement w, bool useBlands);
+
+  /** These fields are designed to be accessible to TheoryArith methods. */
+  class Statistics {
+  public:
+    TimerStat d_initialSignalsTime;
+    IntStat d_initialConflicts;
+
+    IntStat d_fcFoundUnsat;
+    IntStat d_fcFoundSat;
+    IntStat d_fcMissed;
+
+    TimerStat d_fcTimer;
+    TimerStat d_fcFocusConstructionTimer;
+
+    TimerStat d_selectUpdateForDualLike;
+    TimerStat d_selectUpdateForPrimal;
+
+    ReferenceStat<uint32_t> d_finalCheckPivotCounter;
+
+    Statistics(uint32_t& pivots);
+    ~Statistics();
+  } d_statistics;
+};/* class FCSimplexDecisionProcedure */
+
+}/* CVC4::theory::arith namespace */
+}/* CVC4::theory namespace */
+}/* CVC4 namespace */
+