Method attemptToMergeVariables

src/engine/Engine.cpp:1884–1977

}

bool Engine::attemptToMergeVariables( unsigned x1, unsigned x2 )
{
    /*
      First, we need to ensure that the variables are both non-basic.
    */

    unsigned n = _tableau->getN();
    unsigned m = _tableau->getM();

    if ( _tableau->isBasic( x1 ) )
    {
        TableauRow x1Row( n - m );
        _tableau->getTableauRow( _tableau->variableToIndex( x1 ), &x1Row );

        bool found = false;
        double bestCoefficient = 0.0;
        unsigned nonBasic = 0;
        for ( unsigned i = 0; i < n - m; ++i )
        {
            if ( x1Row._row[i]._var != x2 )
            {
                double contender = FloatUtils::abs( x1Row._row[i]._coefficient );
                if ( FloatUtils::gt( contender, bestCoefficient ) )
                {
                    found = true;
                    nonBasic = x1Row._row[i]._var;
                    bestCoefficient = contender;
                }
            }
        }

        if ( !found )
            return false;

        _tableau->setEnteringVariableIndex( _tableau->variableToIndex( nonBasic ) );
        _tableau->setLeavingVariableIndex( _tableau->variableToIndex( x1 ) );

        // Make sure the change column and pivot row are up-to-date - strategies
        // such as projected steepest edge need these for their internal updates.
        _tableau->computeChangeColumn();
        _tableau->computePivotRow();

        _activeEntryStrategy->prePivotHook( _tableau, false );
        _tableau->performDegeneratePivot();
        _activeEntryStrategy->postPivotHook( _tableau, false );
    }

    if ( _tableau->isBasic( x2 ) )
    {
        TableauRow x2Row( n - m );
        _tableau->getTableauRow( _tableau->variableToIndex( x2 ), &x2Row );

        bool found = false;
        double bestCoefficient = 0.0;
        unsigned nonBasic = 0;
        for ( unsigned i = 0; i < n - m; ++i )
        {
            if ( x2Row._row[i]._var != x1 )