By default, every model in Concert Technology is the most general problem type possible. Consequently, it is not necessary to declare the problem type nor to change the problem type, even if you add quadratic constraints to the model or remove them from it. In contrast, both the Callable Library and the Interactive Optimizer need for you to indicate a change in problem type explicitly if you remove the quadratic constraints that make your model a QCP.

In both the Callable Library and Interactive Optimizer, if you want to remove the quadratic constraints in order to solve the problem as an LP or a QP, then you must first change the problem type, just as you would, for example, if you removed the quadratic coefficients from a quadratic objective function.

From the Callable Library, use the routine CPXchgprobtype to change the problem type to CPXPROB_LP if you remove the quadratic constraints from your model in order to solve it as an LP. Contrariwise, if you want to add quadratic constraints to an LP or a QP model and then solve it as a QCP, use the routine CPXchgprobtype to change the problem type to CPXPROB_QCP.

When using the Interactive Optimizer, you apply the command change problem with one of the following options: