Prevent cycling

src/engine/Engine.cpp

@@ -312,6 +312,7 @@ void Engine::performSimplexStep()
     unsigned tries = GlobalConfiguration::MAX_SIMPLEX_PIVOT_SEARCH_ITERATIONS;
     Set<unsigned> excludedEnteringVariables;
     unsigned bestLeaving = 0;
+    double bestChangeRatio = 0.0;
 
     while ( tries > 0 )
     {
@@ -340,6 +341,7 @@ void Engine::performSimplexStep()
         {
             bestEntering = _tableau->getEnteringVariableIndex();
             bestLeaving = _tableau->getLeavingVariableIndex();
+            bestChangeRatio = _tableau->getChangeRatio();
             memcpy( _work, _tableau->getChangeColumn(), sizeof(double) * _tableau->getM() );
             break;
         }
@@ -352,6 +354,7 @@ void Engine::performSimplexStep()
             bestEntering = _tableau->getEnteringVariableIndex();
             bestPivotEntry = pivotEntry;
             bestLeaving = leavingIndex;
+            bestChangeRatio = _tableau->getChangeRatio();
             memcpy( _work, _tableau->getChangeColumn(), sizeof(double) * _tableau->getM() );
         }
 
@@ -397,6 +400,7 @@ void Engine::performSimplexStep()
     _tableau->setEnteringVariableIndex( bestEntering );
     _tableau->setLeavingVariableIndex( bestLeaving );
     _tableau->setChangeColumn( _work );
+    _tableau->setChangeRatio( bestChangeRatio );
 
     bool fakePivot = _tableau->performingFakePivot();
 

src/engine/ITableau.h

@@ -121,6 +121,7 @@ class ITableau
     virtual unsigned getLeavingVariable() const = 0;
     virtual unsigned getLeavingVariableIndex() const = 0;
     virtual double getChangeRatio() const = 0;
+    virtual void setChangeRatio( double changeRatio ) = 0;
     virtual bool performingFakePivot() const = 0;
     virtual void performPivot() = 0;
     virtual double ratioConstraintPerBasic( unsigned basicIndex, double coefficient, bool decrease ) = 0;

src/engine/Tableau.cpp

@@ -889,6 +889,11 @@ double Tableau::getChangeRatio() const
     return _changeRatio;
 }
 
+void Tableau::setChangeRatio( double changeRatio )
+{
+    _changeRatio = changeRatio;
+}
+
 void Tableau::computeChangeColumn()
 {
     // _a gets the entering variable's column in A
@@ -1694,9 +1699,30 @@ void Tableau::updateAssignmentForPivot()
     // If the change ratio is 0, just maintain the current assignment
     if ( FloatUtils::isZero( _changeRatio ) )
     {
+        ASSERT( !performingFakePivot() );
+
+        DEBUG({
+                // This should only happen when the basic variable is pressed against
+                // one of its bounds
+                if ( !( _basicStatus[_leavingVariable] == Tableau::AT_UB ||
+                        _basicStatus[_leavingVariable] == Tableau::AT_LB ||
+                        _basicStatus[_leavingVariable] == Tableau::BETWEEN
+                        ) )
+                {
+                    printf( "Assertion violation!\n" );
+                    printf( "Basic (leaving) variable is: %u\n", _basicIndexToVariable[_leavingVariable] );
+                    printf( "Basic assignment: %.10lf. Bounds: [%.10lf, %.10lf]\n",
+                            _basicAssignment[_leavingVariable],
+                            _lowerBounds[_basicIndexToVariable[_leavingVariable]],
+                            _upperBounds[_basicIndexToVariable[_leavingVariable]] );
+                    printf( "Basic status: %u\n", _basicStatus[_leavingVariable] );
+                    printf( "leavingVariableIncreases = %s", _leavingVariableIncreases ? "yes" : "no" );
+                    exit( 1 );
+                }
+            });
+
         double basicAssignment = _basicAssignment[_leavingVariable];
         double nonBasicAssignment = _nonBasicAssignment[_enteringVariable];
-
         _basicAssignment[_leavingVariable] = nonBasicAssignment;
         _nonBasicAssignment[_enteringVariable] = basicAssignment;
         return;

src/engine/Tableau.h

@@ -208,6 +208,7 @@ class Tableau : public ITableau, public IBasisFactorization::BasisColumnOracle
     unsigned getLeavingVariable() const;
     unsigned getLeavingVariableIndex() const;
     double getChangeRatio() const;
+    void setChangeRatio( double changeRatio );
 
     /*
       Returns true iff the current iteration is a fake pivot, i.e. the

src/engine/tests/MockTableau.h

@@ -260,6 +260,8 @@ class MockTableau : public ITableau
     }
 
     double getChangeRatio() const { return 0; }
+    void setChangeRatio( double /* changeRatio */ ) {}
+
     void performPivot() {}
     bool performingFakePivot() const
     {