Continuous-system simulation languages: A state-of-the-art survey

Abstract

Simulation is the art and science of describing the behavior of a dynamic system by means of a model and using this validated model in a series of experiments designed to provide insight into the future behavior of the system under specific conditions. Therefore, the process of simulation can be visualized as consisting of four phases: (1) problem definition, (2) model specification, (3) model validation, and (4) insight acceleration^1 through experimentation. In order to facilitate the process of simulation, one develops various tools. The digital computer is one such tool. Man's interface to the computer is through the language with which he describes his problem to the computer. The ease with which he solves his problem depends upon the richness of the language as well as the ability of the language to be unambiguously specific. In turn, the structure of the language depends on the form of the model to be implemented. However, having to work with a given language may bias or control the form of the model. Therefore, one must be careful in selecting and using computer languages for system simulation. All physical systems exist in the time-space continuum. The type of model one selects depends on the degree of aggregation of individual phenomena. One may choose either a continuous or a discrete approach to model development. Continuous models are useful when the behavior of the system depends more on the aggregate flow of events than upon the occurrence of individual events Choice of the continuous-or discrete- event modeling approach depends on the nature of the system, the objectives of the simulation, and the tools available to implement the simulation. Because of the mathematical nature of the models in continuous system simulation, special languages have been evolued which are specifically adapted to expressing this class of problems. Over forty continuous-system simulation languages have been developed as of 1973. This paper will survey currently available languages (available commercially or from specific research groups) for simulating dynamic systems described by differential equations. The languages surveyed in this paper are partitioned into two groups. The first group consists of general Continuous-System Simulation Languages designed to represent dynamic models defined by sets of differential equations having primarily one independent variable. Included in the first group are MIMIC, DYNAMO, CSMP/CSMP III, CSSL-III, SL-1, and PROSE. The second group consists of languages specifically designed to represent models defined by partial differential equations. Included in the second group are SALEM, PDEL, LEANS, DSS, PDELAN and FORSIM. The objective of this survey is to describe the functional characteristics of currently available continuous-system simulation languages from a user's point of view. Emphasis will be placed on the unique features of the language, the services provided, the degree of supplier support, the degree of generality, flexibility in terms of user ability to extend the language, the ease of learning, and finally the economics of use.