SIMULATION

The article discusses a subject about which much is said and little is written—the writing of specifications for hybrid software. The basis for the article is an Aerospace Corpora tion Hybrid Computing Center study of the upgrading of the digital portion of our hybrid system.

In the process of discussing the study, a philosophy for writing specifications for hybrid software is presented. The philosophy, herein called "Functional Specifications," can be used by any facility regardless of its requirements. With Functional Specifications, a facility states only its require ments and leaves the designing of the system to the vendor.

This paper presents analog, hybrid, and digital simulation techniques for one-dimensional flow, diffusion, and wave- type systems. These techniques also provide the basis for the simulation of more complex distributed-parameter systems. Many of the techniques considered are well known; however some of them are just recently devel oped. The various techniques result from either discretiza tion and transformation of the original partial differential equations or from application of the method of charac teristics. From this point of view, it is possible to fit the

techniques into a general framework. It will be indicated by means of the properties of each technique which type of computer will best implement it and which system can be treated by it most advantageously.

The current concept of the flow chart for documenting a computer program seems to be more heavily influenced by its business data processing background than by its mathematically oriented inception. The result of this is a loss of definition which inhibits further developments in program documentation.

This paper proceeds from an analysis of the structure of a program and how this structure is represented by a flow chart to derive an extension of this: continuous flow charts.

A continuous flow chart, which may be constructed from a conventional flow chart by removing its points of (flow) discontinuity, is shown to be a form of docu mentation ideally suited for large-scale programs that by their nature involve complex logic (such as a war-game simulation).

The motivation for continuous flow charting is the pos sibility of dynamic documentation arising from a set of such flow charts. That is, the requirements suggested in this paper for a flow chart to be called continuous pro vide an inductive definition for the members of a set of levels of documentation of a simulation (such that the ease of a user's level to level transition of understanding [the logic depicted] is maintained). Such a set would have, at its highest level, a flow chart picturing the overall logic of the entire simulation, and, at successively lower levels it would contain flow charts describing smaller portions of the program in greater detail. An actual machine-language program would constitute the lowest level of documentation in this set.

Since the creation of such a set of continuous flow charts can be started from either the highest level or the lowest level, then this procedure should serve equally well for either developing a complex program from its most basic logical conception, or for documenting such a program as has already been written.