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doi: 10.1177/003754977803100101pmid: N/A
Continuous System Simulation Languages (CSSLs) are used to program the simulation of dynamic systems that are described by differential equations. Mini computer-based languages are particularly attractive because they generally provide good man-machine interaction. This paper describes an interactive simulation language, ISIS, which provides many of the facilities hitherto restricted to large computers. ISIS is written in FORTRAN and can easily be imple mented on any computer that accepts FORTRAN IV pro grams (the original version runs on a PDP-8). ISIS is designed to offer the user high-level language facilities in the simplest possible form. Line-by- line syntax checking and the built-in editor allow fast interactive development of programs. The execu tion of a simulation can be interrupted by using special commands that allow the user to change the values of variables, modify or introduce OUTPUT and incremental PLOT statements, and produce 'post-mortem' graphs before continuing the simulation. With these and other interactive features, ISIS provides com prehensive facilities for the study of dynamic sys tems on modest minicomputer configurations.
Standridge, Charles R.; Alan, A.; Pritsker, B.; Delcher, Harry
doi: 10.1177/003754977803100102pmid: N/A
This paper describes the development of a GASP IV simulation of the primary health-care system of Indiana. In the course of this research, other prob lems were found to be as important as the construc tion of the model. These problems included data acquisition and analysis, definition of system per formance measures, the comparison of alternative policies, and the interaction between physicians and system analysts.
doi: 10.1177/003754977803100103pmid: N/A
Theoretical ecology requires simulation because real istic ecosystem models are too complex for mathemati cal analysis. In this paper we propose a way of moving from a complex simulation model based on the "mechanics" of an ecosystem to a much simpler model that exhibits behaviour similar to that of the origi nal model in its major features. The tool used to isolate the key characteristics of the original model is sensitivity analysis. It enables the investigator to identify the variables and parameters that deter mine the essential behaviour of the original model and to formulate a clear picture of that behaviour. With this information in hand, the investigator can devise a simplified model that exhibits the same essential behaviour.While the simplified model behaves like the original model, its inner workings only generally parallel those of the original. Its simplicity allows the investigator to test his intuitive ideas directly, clarifying understanding of the ecosystem originally modelled. Further, the investigator may be able to adapt the simplified model to other similar ecosystems. The methods outlined in this paper are illustrated by a case study of a forest infested by tent caterpillars.
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