Alexander H. Levis

Bio: Alexander H. Levis is an academic researcher from George Mason University. The author has contributed to research in topics: Petri net & Executable. The author has an hindex of 25, co-authored 169 publications receiving 2404 citations. Previous affiliations of Alexander H. Levis include Massachusetts Institute of Technology & University of Kassel.

Optimal linear regulators: The discrete-time case

Abstract: In this paper the optimal discrete-time linear-quadratic regulator problem is carefully presented and the basic results are reviewed. Dynamic programming is used to determine the optimization equations. Special attention is given to problems unique to the discrete-time case; this includes, for example, the possibility of a singular system matrix and a singular control-effort weighting matrix. Some problems associated with sampled-data systems are also summarized, e.g., sensitivity to sampling time, and loss of controllability due to sampling. Computational methods for the solution of the optimization equations are outlined and a simple example is included to illustrate the various computational approaches.

On the behaviour of optimal linear sampled-data regulators†

Abstract: Optimal sampled-data controls for linear processes with quadratic criteria are determined through application of the discrete minimum principle. The effect of sampling on the closed-loop system's performance is investigated and the asymptotic behaviour of the optimal cost for large sampling periods is determined. The resulting design method is applicable to continuous, sampled-data and discrete regulators.

C4ISR Architectures: I. Developing a Process for C4ISR Architecture Design

Abstract: The C4ISR Architecture Framework document issued by the Department of Defense specifies three views of an information architecture and defines a set of products that describe each view. These architecture views are to serve as the basis for C4ISR system development and acquisition. The Framework does not provide a process for architecture design. In this paper, information architectures are described in the context of Structured Analysis, and then the architecture views of the Framework and the related products are interpreted in that context. A methodology for architecture design is developed that is then implemented using Structured Analysis and object orientation in two companion papers. © 2000 John Wiley & Sons, Inc. Syst Eng 3: 225‐247, 2000

Petri net representation of decision models

Abstract: Models of decision-making organizations supported by command, control, and communication systems are represented using the Petri net formalism. A small set of primitives, defining the correspondence between decision models, signals, and functions and their Petri net counterparts, is proposed. A new decision signal-routing demultiplexer is added to the Petri net formalism to represent internal decision-making in the model. Using the above primitives, any decision-making structure can be modeled by a Petri net diagram. An array is introduced that describes the interactions between decision-makers, and an algorithm is presented for the calculation of delay when synchronous protocols are used.

Petri nets: Properties, analysis and applications

Abstract: Starts with a brief review of the history and the application areas considered in the literature. The author then proceeds with introductory modeling examples, behavioral and structural properties, three methods of analysis, subclasses of Petri nets and their analysis. In particular, one section is devoted to marked graphs, the concurrent system model most amenable to analysis. Introductory discussions on stochastic nets with their application to performance modeling, and on high-level nets with their application to logic programming, are provided. Also included are recent results on reachability criteria. Suggestions are provided for further reading on many subject areas of Petri nets. >

Nineteen Dubious Ways to Compute the Exponential of a Matrix, Twenty-Five Years Later ⁄

Abstract: In principle, the exponential of a matrix could be computed in many ways. Methods involving approximation theory, differential equations, the matrix eigenvalues, and the matrix characteristic polyn...

Feedback Systems: An Introduction for Scientists and Engineers

Abstract: This book provides an introduction to the mathematics needed to model, analyze, and design feedback systems. It is an ideal textbook for undergraduate and graduate students, and is indispensable for researchers seeking a self-contained reference on control theory. Unlike most books on the subject, Feedback Systems develops transfer functions through the exponential response of a system, and is accessible across a range of disciplines that utilize feedback in physical, biological, information, and economic systems. Karl strm and Richard Murray use techniques from physics, computer science, and operations research to introduce control-oriented modeling. They begin with state space tools for analysis and design, including stability of solutions, Lyapunov functions, reachability, state feedback observability, and estimators. The matrix exponential plays a central role in the analysis of linear control systems, allowing a concise development of many of the key concepts for this class of models. strm and Murray then develop and explain tools in the frequency domain, including transfer functions, Nyquist analysis, PID control, frequency domain design, and robustness. They provide exercises at the end of every chapter, and an accompanying electronic solutions manual is available. Feedback Systems is a complete one-volume resource for students and researchers in mathematics, engineering, and the sciences.Covers the mathematics needed to model, analyze, and design feedback systems Serves as an introductory textbook for students and a self-contained resource for researchers Includes exercises at the end of every chapter Features an electronic solutions manual Offers techniques applicable across a range of disciplines

Nineteen Dubious Ways to Compute the Exponential of a Matrix

Abstract: In principle, the exponential of a matrix could be computed in many ways. Methods involving approximation theory, differential equations, the matrix eigenvalues, and the matrix characteristic polyn...