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doi: 10.1177/003754978905300203pmid: N/A
A Turbo Pascal-based simulator specifically designed for continuous-time models with time delays and hysteretic phenomena is presented and its use illustrated with examples. Delays can be time- and state-dependent.For models with hysteretic (multi-valued) behavior, use is made of a recently introduced mathematical paradigm: the differential automaton. For models defined by differ ential or delay-differential equations with jumps in the derivatives, the differential automaton formalism can be bypassed by using a switch function to indicate points of low differentiability in the model. The switch function interacts with the simulator to approximate each point of discontinuity where the numerical integrator is to be reini tialized. This interaction, transparent to the user and implemented via side effects of the switch function, replaces the explicit scheduling of state events by the user.For models with time delays, a global approximation is constructed for each delayed state variable. Each global ap proximation is partitioned into sufficiently smooth seg ments and a smoothness index is associated with the boundary separating any two such segments. Whenever a delay crosses between two adjacent segments, should the value of the smoothness index require it, the time of crossing is approximated iteratively, the numerical integra tor is reinitialized, and a new segment is started in the partition. A new segment is also started whenever a switching takes place.The simulator graphical output interface is self-config uring at execution time with respect to the video display adapter-display combination in use. Interactive plotting programs with on-line documentation are also provided to retrieve, then plot, problem data from save files generated during a simulation.
Hitz, Martin; Werthner, Hannes; Guariso, Giorgio
doi: 10.1177/003754978905300204pmid: N/A
The conceptual design and a prototype implementation of a knowledge based interactive genera tor of simulation models is pre sented. The system administrates several components, among them a model base, a knowledge-base, and a data base. Emphasis is laid on the integration of the model and the knowledge base. This connection of numeric and knowledge representa tion components is one of the main advantages of the system. A frame based approach has been chosen for the semantic representation of the simulated models. The prototype has been implemented on a XEROX 1186 workstation and takes advan tage of the presence of two proces sors : a LISP processor managing the logical description, selection, and maintenance of models as well as the overall control of the system, and an 8088 processor to run the simulation programs that are written in classical programming languages like FORTRAN. The system is designed to free the scien tific expert from details about computer science and to let him concentrate on the actual simulation problems.
doi: 10.1177/003754978905300205pmid: N/A
The energy-systems language method of modelling and simula tion, because of its energy con strained rules, is a means for trans ferring homologous concepts be tween levels of the hierarchies of nature. Mathematics of self-organi zation may justify "emulation" as the simulation of systems overview without details. Here, these methods are applied to the new fields of "ecological economics" and "ecological engineering." Since the vitality of national economies depends on the symbiotic coupling of environmental resources and human economic behavior, the energy language is adapted to develop overview models of nations relevant to public policies. An overview model of a developing nation is given as an example with simulations for alternative policies. Maximum economic vitality was obtained with trade for external resources, but ultimate economic carrying capacity and standard of living was determined by indige nous resources, optimum utilization and absence of foreign debt.
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