Simulation of Control Systems

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Center, Univ. of Maryland, College Park, MD,. TR-887, Apr. 1980. .... for those who wish to know the state-of-the-art of system modeling and simulation. ... Weizmann Institute of Science (Rehovot, Israel, August 13-18, 1978). It is actually one of ...
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IEEE TRANSACTIONS ON SYSTEMS,

several subiterations at each iteration in order to find the maximum feasible X(x, y): starting from a small initial X, computing F(x, y) and the associated cost, incrementing X, and repeating the process as long as the cost keeps decreasing. Other descent techniques such as the conjugate gradient method would require less computation but more storage. Other optimization methods, such as nonlinear Gauss-Seidel iteration, might be more effective. VII. CONCLUDING REMARKS Image smoothing and segmentation can often be achieved by constructing a piecewise constant function whose pieces correspond to the desired regions. We have used the method of steepest descent to construct such a function having minimum roughness and minimum discrepancy from the original image. If we know that there should be only two types of regions, light and dark, we can use discrepancy from a thresholded image, or better, closeness to the mean gray level, as a cost component in place of discrepancy from the original image. The latter method yields results very similar to those obtained by relaxation methods, but without the need to introduce "probabilities" that the pixels belong to the two types of regions. It would be of interest to apply a similar approach based on cost function minimization to other problems, such as edge and curve enhancement, that have been successfully handled using relaxation methods.

MAN,

AND CYBERNETICS, VOL.

SMC-12,

NO.

1, JANUARY/FEBRUARY 1982

In summary, we have investigated the possibility of deriving simple piecewise constant approximations to an image by cost function minimization, using two types of images (tank and terrain). This approach yields results similar to those obtainable by various other methods. It is of conceptual interest, but it does not seem to be of great practical value because of its relatively high computational cost.

REFERENCES [1l

A. Martelli and U. Montanari, "Optimal smoothing in picture processing: an application to fingerprints," in Proc. IFIP Congr., 1971, Booklet TA-2,

pp. 86-90.

[2] J. S. Weszka and A. Rosenfeld, "Threshold evaluation techniques," IEEE Traits. Svst., Mani, Cvhernt., vol. SMC-8. pp. 622-629, 1978. [31 P. R. Beaudet, "Rotationally invariant image operators," in Proc. 4th loit. Joinit Coatf. on1 Puttern Recognitioni, 1976, pp. 579-583. [41 L. Kitchen and A. Rosenfeld, "Gray level corner detection," Comput. Vision Lab., Comput. Sci. Center, Univ. of Maryland, College Park, MD, TR-887, Apr. 1980. 51 0. Faugeras and M. Berthod, "Scene labeling: An optimization approach," Patterit Recognition. vol. 12, pp. 339-347, 1980. [61 M. Berthod and 0. Faugeras, "Using context in the global recognition of a set of objects: An optimization approach." in lpiforniautioi Processing 80, S. H. Lavington. Ed. Amsterdam, The Netherlands: 1980, pp. 695-698. [71 R. Smith and A. Rosenfeld. "Thresholding using relaxation," IEEE Trans. Putte-i Atial. Macdhiune lIitell., vol. PAMI-3, 1981, pp. 598-606.

Book Reviews Modem Power System Analysis-I. J. Nagrath and D. P. Kothari (New Delhi, India: Tata McGraw-Hill Ltd., 1980, 375 pp.). Reviewed by R. C. Desal, Department of Electrical Engineering, M.S. Universitv of Baroda, Vadodara 390001, India. Modern power systems, owing to their interconnected, complex, and integrated natures, are assuming the proportions of large-scale systems. As such, the solutions of their problems have to be obtained by using the latest computer-oriented techniques devised for large-scale systems and the undergraduate electrical engineering students and the practicing power-system engineers must be trained accordingly to keep them abreast of rapid developments in the field. Most of the books written before the last decade lack the modern approach to power-system analysis. The few books written by power engineers during the last decade discuss only a few aspects of modern techniques. However a person with a background in control system engineering is better suited to write a book on "Power System Analysis," with the large-scale systems approach. Thus Professor Nagrath (coauthor of a book titled Cotntrol Svstems Eniginzeering, published by Wiley Eastern Limited) in association with Professor Kothari has done a very thorough job of writing this book which satisfies the stated need by integrating the basic principles of power-system analysis (illustrated through simple system structures) with analysis techniques for the large-scale systems found in practice. The book contains the following topics: Inductance, resistance and capacitance of transmission lines, representation of power-system components, characteristics and performance of power transmission lines, load flow studies, optimal system operation, automatic generation and voltage control, economic dispatch, symmetrical fault analysis and symmetrical components, unsymmetrical fault analysis, and power-system stability. This book includes digital-computer algorithms for various system studies such as load flow, fault level analysis, stability, etc. As a special

feature it also covers the latest and practically useful topics such as unit commitment, generation reliability, optimal thermal scheduling, optimal hydro-thermal scheduling, and decoupled load flow. In essence the book is highly comprehensive, well-organized, up-to-date and (above all) lucid and easy to follow for self-study. The book is amply illustrated with solved examples for every concept and technique employing two-, three-, or four-bus structure, as necessary and the numerous examples given at the end of each chapter makes it a very useful text for teaching purposes. The reviewer rates this book highly and recommends it to students and practicing engineers in power systems. He congratulates the authors for carrying out a splendid job.

Simulation of Control Systems-I. Troch, Ed. (Amsterdam, Netherlands and New York: North-Holland, 1978, pp. 311). Reviewed bv S. G. Tzafestas, Cotitrol Systems Laboratory, Universitv of Patras, Greece. This book contains the papers presented at the International Association for Mathematics and Computers in Simulation Symposium on "Simulation of Control Systems with Emphasis on Modelling and Redundancy," held at the Technical University of Vienna (Sept. 27-29,

1978).

The contributed papers have been arranged according to their main subject in three sections. A separate section involves the invited papers by R. Tomovic, H. Rzehak, E. Pavlik, and R. Vichnevetsky. These papers give important surveys on the control of large systems, redundancy in hardware and software of process computers, interdependence of process model and simulation tool, and the difficulties of computing optimal control problems.

IEEE TRANSACTIONS ON SYSTEMS, MAN, AND

CYBERNETICS, VOL. SMC-12, NO. 1, JANUARY/FEBRUARY 1982

Section I (Theoretical aspects of modelling and simulation) involves contributions on pulse-modulated control systems, large-scale systems design, and some theoretical aspects. Section 2 (Software for simulation of control systems) contains the works on data transmission and handling and software for the simulation of general and particular control systems. Finally, Section 3 (Modelling and simulation of specific systems) contains a variety of applications in electrical systems, chemical processes, nuclear engineering, transportation systems, biological systems, socioeconomic systems, etc. Most of the sixty-two papers included present new and important ideas, techniques, and results for a broad spectrum of topics within the modelling, simulation, and control field which make the book a useful source for the researcher and practitioner in this field. Moreover the surveys which are included make the book valuable for those who wish to know the state-of-the-art of system modeling and simulation. Methodology in Systems ModeDing and Simulation-B. Zeigler, M. Ezas, G. Klir and T. Oren, Eds. (Amsterdam, The Netherlands and New York: North-Holland, 1979, pp. 537). Reviewed by S. G. Tzafestas, Control Systems Laboratory, University of Patras, Greece.

This book contains "selected refereed papers from those presented at the Symposium on Modelling and Simulation Methodology," held at the Weizmann Institute of Science (Rehovot, Israel, August 13-18, 1978). It is actually one of the first books devoted entirely to the methodology of modelling and presents new important ideas for constructing, validating, and organizing models of complex, multipurpose, large-scale, interdisciplinary systems.

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It is organized in six sections. Section I (Conceptual Base) provides four useful frameworks for solving modelling and simulation problems. Section 2 (Multifaceted Modelling: Approaches and Issues) is devoted to interdisciplinary situations such as energy systems, ecosystems, socioeconomic systems and federal management of modelling processes. Section 3 (Software Tools for Model Construction) presents the current status.of simulation languages and systems which provide the basic tools for model description and building in advanced methodologies. Section 4 (Structure Identification and Model Calibration) is devoted to the particular aspect of searching through the candidate model space in an uncertain of limited data-quality environment. Among the systems considered are social systems, ecosystems, and biochemical (gluconeogenesis) systems. Section 5 (Modelling Methodology in Design) considers some approaches to computer system and software design ranging from sophisticated simulation languages, to real-time process control modelling, and designs subject to manufacturing tolerances, and material and environmental uncertainties. Finally, Section 6 (Theory in Modelling and Simulation) presents some aspects towards a theoretical formalism of statistical and other modelling methodology. There are included increasingly structural approaches to model simplification as well as some views on general systems theory as a synthesis of holism and reductionism. The book concludes with the various opinions expanded in the closing panel discussion on "future of modelling methodology: Which roads to take?" and a list of the other papers presented at the symposium. In addition, a useful set of reviews of readings, relevant to modelling and simulation, is provided. The mnaterial of this carefully edited book is valuable not only to the expert in the field but also to the nonexpert who wishes to learn and use the developments in systems modelling and simulation.

Contributors Fredric N. Bailey (S'59-M'63) received the B.S.

degree in electrical engineering from Purdue Uni-

versity, West Lafayette, IN, in 1953, and the M.S. and Ph.D. degrees from the University of Michigan, Ann Arbor, in 1960 and 1964, respecFrom 1953 to 1957 he was employed by the United States Navy as a pilot and Electronics Officer. In 1957 he joined the Cooley Electronics Laboratory of the Department of Electrical Engineering, the University of Michigan, working on nonlinear problems in signal processing and control. Since 1964 he has been with the Department of Electrical Engineering at the University of Minnesota, Minneapolis, where he is currently an Associate Professor. He also holds joint appointments in Control Sciences and Computer Sciences. Since 1966 he has been a consultant in systems analysis and signal processing to the UNIVAC Division of the Sperry Rand Corporation. His research interests include systems theory, control theory, distributed control systems, and signal processing with emphasis on computer applications in these areas.

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James R. Burns (S'71-M'73) received the B.S. degree from the University of Colorado, Boulder, in 1966, and the M.S. and Ph.D degrees from Purdue University, West Lafayette, IN, in 1967 and 1973, respectively. Since then he has affiliated himself with Texas Tech University, Lubbock. He is currently an Associate Professor of Systems and Computer Science in the College of Busir'ess Administration. He regularly teaches courses in management science including mathematical programming,

simulation, and decision theory. He is the author of numerous articles on the use of structural models to formulate dynamical simulations. Recently, he has served as a consultant to Sandia Laboratories and to Texas Instruments. He is interested in applications of simulation to energy/economic problems, production, and inventory control. Dr. Burns is a member of Tau Beta Pi, Sigma Tau, the Institute of Management Science, and the American Institute of Decision Science.

Frank Di Cesare (M'63) received the B.S. and M.S. degrees in electrical engineering from Northeastern University, Boston, MA, in 1960 and 1962, respectively, and the Ph.D. degree from Carnegie-Mellon University, Pittsburgh, PA, in 1970. He was at Carnegie-Mellon University from 1964 to 1969, serving as an Instructor in electrical engineering for two years and subsequently as an Assistant Research Engineer at the Transportation Research Institute. In 1969 he joined the Rensselaer Polytechnic Institute faculty in Troy, NY where he is now an Associate Professor of Electrical, Computer, and Systems Engineering and coordinates the activities of the Laboratory for Computer Methods in Large Scale Systems and a graduate program in Large Scale Systems. His current research interests include modeling in land use, transportation and environmental systems; and the design, development, and evaluation of public sector decision support systems. His various consulting assignments have included local and state government agencies as well as development corporations; and he is involved in the activities of the Transportation Research Board.