/// <summary>
/// Do a pivot. Move entryVar into the basis and move exitVar
/// out of the basis.
/// </summary>
/// <remarks>
/// We could for example make entryVar a basic variable and
/// make exitVar a parametric variable.
/// </remarks>
protected void Pivot(ClAbstractVariable entryVar, ClAbstractVariable exitVar)
/* throws ExClInternalError */
{
// the entryVar might be non-pivotable if we're doing a
// RemoveConstraint -- otherwise it should be a pivotable
// variable -- enforced at call sites, hopefully
ClLinearExpression pexpr = RemoveRow(exitVar);
pexpr.ChangeSubject(exitVar, entryVar);
SubstituteOut(entryVar, pexpr);
AddRow(entryVar, pexpr);
}
