Problem definition with the help of Graphical User Interface. The Graphical User Interface (GUI) guides the user during problem definition or modification. The user must provide the different terms regarding the problem and the desired solution approach. Figure (A) on the left shows an screen where the optimization options are set (with NLP settings, gradient method, performance index, and bounds on the control variables and on time-independent parameters). Figure (B) illustrates how the user can introduce the systems dynamics and related options, such as initial conditions, fixed parameters.