src/theory/arith/attempt_solution_simplex.h

   1 /*********************                                                        */
   2 /*! \file simplex.h
   3  ** \verbatim
   4  ** Original author: taking
   5  ** Major contributors: none
   6  ** Minor contributors (to current version): kshitij, mdeters
   7  ** This file is part of the CVC4 prototype.
   8  ** Copyright (c) 2009-2012  New York University and The University of Iowa
   9  ** See the file COPYING in the top-level source directory for licensing
  10  ** information.\endverbatim
  11  **
  12  ** \brief This is an implementation of the Simplex Module for the Simplex for DPLL(T)
  13  ** decision procedure.
  14  **
  15  ** This implements the Simplex module for the Simpelx for DPLL(T) decision procedure.
  16  ** See the Simplex for DPLL(T) technical report for more background.(citation?)
  17  ** This shares with the theory a Tableau, and a PartialModel that:
  18  **  - satisfies the equalities in the Tableau, and
  19  **  - the assignment for the non-basic variables satisfies their bounds.
  20  ** This is required to either produce a conflict or satisifying PartialModel.
  21  ** Further, we require being told when a basic variable updates its value.
  22  **
  23  ** During the Simplex search we maintain a queue of variables.
  24  ** The queue is required to contain all of the basic variables that voilate their bounds.
  25  ** As elimination from the queue is more efficient to be done lazily,
  26  ** we do not maintain that the queue of variables needs to be only basic variables or only
  27  ** variables that satisfy their bounds.
  28  **
  29  ** The simplex procedure roughly follows Alberto's thesis. (citation?)
  30  ** There is one round of selecting using a heuristic pivoting rule. (See PreferenceFunction
  31  ** Documentation for the available options.)
  32  ** The non-basic variable is the one that appears in the fewest pivots. (Bruno says that
  33  ** Leonardo invented this first.)
  34  ** After this, Bland's pivot rule is invoked.
  35  **
  36  ** During this proccess, we periodically inspect the queue of variables to
  37  ** 1) remove now extraneous extries,
  38  ** 2) detect conflicts that are "waiting" on the queue but may not be detected by the
  39  **  current queue heuristics, and
  40  ** 3) detect multiple conflicts.
  41  **
  42  ** Conflicts are greedily slackened to use the weakest bounds that still produce the
  43  ** conflict.
  44  **
  45  ** Extra things tracked atm: (Subject to change at Tim's whims)
  46  ** - A superset of all of the newly pivoted variables.
  47  ** - A queue of additional conflicts that were discovered by Simplex.
  48  **   These are theory valid and are currently turned into lemmas
  49  **/
  50
  51
  52 #include "cvc4_private.h"
  53
  54 #pragma once
  55
  56 #include "util/statistics_registry.h"
  57 #include "theory/arith/simplex.h"
  58 #include "theory/arith/approx_simplex.h"
  59
  60 namespace CVC4 {
  61 namespace theory {
  62 namespace arith {
  63
  64 class AttemptSolutionSDP : public SimplexDecisionProcedure {
  65 public:
  66   AttemptSolutionSDP(LinearEqualityModule& linEq, ErrorSet& errors, RaiseConflict conflictChannel, TempVarMalloc tvmalloc);
  67
  68   Result::Sat attempt(const ApproximateSimplex::Solution& sol);
  69
  70   Result::Sat findModel(bool exactResult){
  71     Unreachable();
  72   }
  73
  74 private:
  75   bool matchesNewValue(const DenseMap<DeltaRational>& nv, ArithVar v) const;
  76
  77   bool processSignals(){
  78     TimerStat &timer = d_statistics.d_queueTime;
  79     IntStat& conflictStat  = d_statistics.d_conflicts;
  80     return standardProcessSignals(timer, conflictStat);
  81   }
  82   /** These fields are designed to be accessible to TheoryArith methods. */
  83   class Statistics {
  84   public:
  85     TimerStat d_searchTime;
  86     TimerStat d_queueTime;
  87     IntStat d_conflicts;
  88
  89     Statistics();
  90     ~Statistics();
  91   } d_statistics;
  92 };/* class AttemptSolutionSDP */
  93
  94 }/* CVC4::theory::arith namespace */
  95 }/* CVC4::theory namespace */
  96 }/* CVC4 namespace */
  97