This section tells you how to use the Callable Library in your own applications. Briefly, you must initialize the ILOG CPLEX environment, instantiate a problem object, and fill it with data. Then your application calls one of the ILOG CPLEX optimizers to optimize your problem. Optionally, your application can also modify the problem object and re-optimize it. ILOG CPLEX is designed to support this sequence of operations - modification and re-optimization of linear or quadratic programming problems (LPs or QPs) - efficiently by reusing the current basis of a problem as its starting point (when applicable). After it finishes using ILOG CPLEX, your application must free the problem object and release the ILOG CPLEX environment it has been using. The following sections explain these steps in greater detail.