The referenced IloExtractable has not been extracted by the IloAlgorithm

Answer

An IloExtractable is the base class for all of the modeling objects used to build and solve models. Examples include the IloNumVar, IloNumRange, IloConstraint, and IloStateFunction classes (the latter, as of this writing, used by CP-Optimizer but not CPLEX), This error message indicates that you are trying to access an extractable that has not been extracted by the instance of IloAlgorithm mentioned in the error message. This condition can occur in many different situations, including:

• an attempt to access the value of a variable that was not extracted;
• the use of an unextracted extractable in a goal.

• The extractable has not been added to the model, either explicitly via the IloModel::add() function, or implicitly because it is referenced by another extractable (e.g. an IloNumVar referenced by an IloRange or IloConstraint).
• The extractable is not incident to any other extractable. For example, an instance of IloNumVar is incident to an instance of IloRange if the instance of IloNumVar is part of the instance of IloExpr that defines the instance of IloRange.
• This extractable is incident to an extractable, but with no effect on it. For example, the unaffected extractable is used as a variable with a coefficient of zero in a constraint.

• Systematically comment out code that builds the model, thus reducing the number of extractables in the model. When the error disappears after commenting out a particular model building section of code, one or more extractables associated with that code segment are probably involved in the error.
• Make good use of the methods of the IloExtractable class that identify the particular subclass for the individual extractable, such as isVariable() and isConstraint().
• Use the getID() and getName()/setName() methods of the IloExtractable class to more precisely identify the problematic extractable. Or, use the address listed in the error message to identify the extractable.
• Use the << operator provided in the Concert API to display the model and relevant individual extractables.