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This paper is concerned with the concepts of the computer simulation of cybernetic systems. Engineers, sociologists, business men, economists, architects and most recently health scientists have found a need for simulating systems so that their behavior may be predicted and finally controlled. This paper points out the importance of simulation and how simulation is carried out. In particular, it discusses the control of man and machine systems which Norbert Wiener and his colleagues at M.I.T. called Cybernetic systems. With regard to man controlled systems, the simulation of a tumer cell in water is considered on an Analog Computer. Particular attention is given to man's direct control of the biological system on the computer and the organization of the differential equations. Also discussed is the simulation of a feedback oscillator having a non-linear active element. This simulation was carried out on both an analog and digital computer. Emphasis is placed on the use of the Hytran Simulation Language (HSL) used in the simulation. To give greater depth to the discussion, a simulation of a traveling repairman is given. This simulation may be applied to health systems also, with some imagination. Although the examples used to demonstrate simulation are in the areas of biology, electronics, and business, there is no reason why these computers cannot be utilized in many other areas from sociology to health. This fact is continually pointed out in the paper with the hope that the reader will create an analogy between those systems considered and his particular system.

Two types of errors which occur in the numerical simulation of gradually varied, unsteady open-channel flows are investigated in this paper: (1) errors resulting from the choice of the momentum equation; and (2) errors resulting from the degree of numerical sophistication of integration techniques used in solving the governing equations by the specified intervals scheme of the method of characteristics. It was found that three different momentum equations cited in the literature give identical results when the velocity distribution is uniform. When this distribution is not uniform, each equation gives somewhat different flow depths for similar initial and boundary conditions of gradually varied, unsteady flow. An increase in complexity of the integration technique increases the accuracy of simulation. To determine the absolute values of accuracy of a technique, the development of accurate flow measuring devices and corresponding experiments are needed for comparison between the results of numerical and physical simulations.

This paper gives a brief overview of some of the present problems and achievements in cardiovascular modeling. Typical of most of the simulations described is a level of complexity such that all-analog simulation often requires too much equipment and all-digital simulation is often too slow. Thus, with today's technology, a hybrid computer is an essential simulation tool. Fortunately, in both the case of multiple model simulation, and that of parameter estimation, the describing equations may be logically divided into groups suitable for solution on the two parts of a hybrid computer, with the overall result that real time operation, or faster, is possible.

This paper presents a “hybrid” method of numerical simulation of collisionless plasmas in which weighted particles are advanced as in particle simulations, but in which the distribution function is reconstructed periodically by a local averaging operation as in numerical solutions of the Vlasov equation. The rates of diffusion resulting from repeated averaging of the distribution function are estimated. These rates indicate that it is possible to minimize the effects of both beaming instabilities and diffusion by properly choosing the frequency of reconstruction of the distribution function. A computer code was written to implement this method and numerical solutions of two-stream instability problems are presented.