Design and use of dynamic modeling in ASCEND IV

Abstract: "We present an alternative design for communicating information between an interactive, equation-based modeling environment user and an intial value problem (IVP) solver. The design is practically demonstrated by connecting the widely available integrator LSODE and the freely available plotting program Xgraph to the ASCEND IV modeling environment. In contrast to the ASCEND III integrator interface, this new design allows an order of magnitude improvement in the ease of developing an understanding of a dynamic model's behavior. The improvement is in part achieved by allowing the user to interactively define what time varying quantities should be recorded for postprocessing by graphics packages or other tools without requiring that a new ASCEND model be compiled, thus making visualization easy. The more significant improvement, however, is the new ability to select any part of the complete dynamic model and solve it, thus making exploration of component dynamic behaviors easy. Finally, the user may interactively change a variable between algebraic and dynamic (state or derivative) roles. This makes it possible to negotiate a solution to the index problems which frequently arise in chemical engineering."