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Tam, Wing Cheung; Karplus, Walter J.
doi: 10.1177/003754977402200202pmid: N/A
Hydrologic systems, like most environmental systems, are usually characterized by partial differential equations. In order to develop a suitable mathe matical model for the analysis of such systems, it, is first necessary to make use of observed data in order to identify or estimate the system parameters. The digital simulation language PDEL has been ex tended so as to facilitate this type of parameter identification. The extended version of the lan guage has been named PDEL-ID. In this paper, two hydrologic modeling problems taken from recent water-resource studies are used as examples to illustrate the parameter identification facilities of PDEL. The solution of these two problems demon strates that little programming effort and virtually no knowledge of optimization techniques are required.
doi: 10.1177/003754977402200203pmid: N/A
In this paper a review of the approaches to modelling adopted by programming languages currently available for discrete-system simulation leads to a close look at some of the advantages of languages which employ an "activity scan." These advantages include faster run-times for highly interrelated systems, simpler event routines, and increased security for the model. Decision tables provide a clear and concise format for specifying a complex set of conditions and the various consequent courses of action. They are therefore ideal for describing the conditions for interaction between component parts of a model as specified in the user-defined event routines. A preprocessor to make decision tables computer- readable would greatly enhance the process of modeZ ling and would allow a considerable extension of the range of conditioned statements to be used in the condition stubs of the table. A decision-table facility would form a useful extension to the many event-oriented simulation programming languages.
doi: 10.1177/003754977402200204pmid: N/A
Procedures are derived for sampling two variables, x and y, which have a predetermined correlation coefficient and possibly have prespecified marginal distributions. Instead of specifying a particular value for the correlation coefficient, the linear correlation or the dependence may be maximized.
Corripio, A.B.; Smith, C.L.; Murrill, P.W.
doi: 10.1177/003754977402200207pmid: N/A
The frequency response of a linear digital control system is studied by simulating a plant (represented by a first-order lag plus dead-time) on the analog computer. The digital controller is simulated with analog track-and-store units and parallel logic components. The high speed of the analog computer allows it to display the sinusoidal signals on an oscilloscope in order to observe instantaneously the effect on the frequency response of changing various system parameters. This paper describes the simulation techniques we used, the results we obtained, and how the analog simulation helped us to get the "big picture" of the problem in only a few hours of simulation runs. We turned to analog simulation only after spending several months in an unsuccessful attempt to solve the problem by digital simulation. The reasons for this lack of success are cited.
doi: 10.1177/003754977402200208pmid: N/A
It does not seem widely known that there exists a number of diode circuits which do not exhibit 1/2-volt errors but do contain pots whose settings can be precalculated. This paper gives eleven such circuits which are admirably suited for the simula tion of nonlinearities on 10-volt analogue computers that have digitally set pots.
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