# Institute for Systems Research Technical Reports

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This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.

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Item Ambiguous Behavior of Logic Bistable Systems(1975-10-04) Hurtado, Marco; Elliott, David L.The standard specification of logic bistable devices do not specify the behavior under conditions in which the input is logically undefined or in which certain kinds of multiple input changes occur. These conditions are unavoidable in logic synchronizers and arbiters. A general deterministic model of bistable devices is proposed, consisting of a non-liner differential system with some adequate properties. Analysis of this model shows that bistable devices can be driven into a logically undefined region by certain admissible inputs and can remain in this region for an unbounded length of time.Item Decomposition and Stability of Multiparameter Singular Perturbation Problems.(1985) Abed, Eyad H.; ISRTime-scale separation and stability of linear time-varying and time-invariant multiparameter singular perturbation problems are analyzed. The first problem considered in the paper is that of deriving upper bounds on the small parasitic parameters ensuring the existence of an invertible, bounded transtormation exactly separating test and slow dynamics. This problem is most interesting for the time-varying case. The analysis of this problem in the time-varying case requires the two time-scale setting introduced by H.IC. Khalil and P.V. Kokotovic (SLIAM J. Control Optim., 17, 56-65, l979). This entails that the mutual ratios of the small parameters are bounded by known positive constants. The second problem considered is to derive parameter bounds ensuring that the system in question is uniformly asymptotically stable. The results on decomposition are used to facilitate the derivation of these latter bounds. Fortunately, the analysis of decomposition and stability questions for time- invariant multiparameter singular perturbation problems requires no restriction on the relative magnitudes of the small parameters. A concept of 'strong D-stability' is introduced and shown to greatly simplify the stability analysis of time- invariant multiparameter problems.Item Estimation of the Rate of a Discrete-Time Multivariate Point Process.(1985) Gubner, John A.; Narayan, P.; ISRWe introduce the notion of a discrete-time multivariate point process which can arise in the modeling of an optical communication system. We wish to estimate the rate of this process at time t given the past of the process up to time t-l. This requires the computation of a certain conditional expectation: we perform this computation by introducing an absolutely continuous change of measure and then applying the generalized Bayes' rule.Item Stability of Multiparameter Singular Perturbation Problems with Parameter Bounds, I. Time-Varying Systems with Cone-Restricted Perturbations.(1985) Abed, Eyad H.; ISRExplicit upper bounds are obtained for the singular perturbation parameters of a general uniformly asymptotically stable multiparameter singularly perturbed system. The study focuses on the linear time-varying case studied by H. K. Khalil and P.V. Kokotovic (SIAM J. Control Opt., 17, 56-65, 1979) in which the small parameters are constrained to have bounded mutual ratios. An upper bound is obtained on a weighted norm of the vector of singular perturbation parameters such that uniform asymptotic stability is ensured if this bound is met. The derivation makes liberal use of Liapunov function arguments. In a companion paper [2], it is shown that for linear time-invariant systems the 'bounded mutual ratios' assumption can be lifted, and typically less conservative parameter estimates are obtained.Item A Superlinearly Convergent Method of Feasible Directions for Optimization Problems Arising in the Design of Engineering Systems.(1985) Panier, E.R.; Tits, A.L.; ISROptimization problems arising from engineering design problems often involve the solution of one or several constrained minimax optimization problems. It is sometimes crucial that all iterates constructed when solving such problems satisfy a given set of 'hard' inequality constraints, and generally desirable that the (maximum) objective function value improve at each iteration. In this paper, we propose an algorithm of the sequential quadratic programming (SQP) type that enjoys such properties. This algorithm is inspired from an algorithm recently proposed for the solution of single objective constrained optimization problems. Preliminary numerical results are very promising.Item Convergence of Implicit Discretization Schemes for Linear Differential Equations with Application to Filtering.(1985) Piccioni, M.; ISRThis paper presents a generalization of results on convergence and robustness of discretization schemes for nonlinear filtering proposed by Kushner. This is made possible by a general theorem on the convergence of semigroups of operators on a Banach space, which gives sufficient conditions for a semidiscretization scheme to remain convergent, once the time is implicitly discretized. As a consequence, sufficient conditions can be given for selecting space discretizations of the state process generator to construct computable nonlinear filters converging to the optimal one.Item Homogenization And Control Of Lattice Structures.(1985) Blankenehip, Gilmer L.; ISRUnder certain natural conditions the dynamics of large, low-mass lattice structures with a regular infrastructure are well approximated by the dynamics of continua, e.g., trusses may be modeled beam equations. Using a technique from the mathematics of asymptotic analysis called homogenization, we show how such approximations may be derived in a systematic way which avoids errors made using "direct" averaging methods. We also develop a model for the combined problem of homogenization and control of vibrations in lattice structures and present some preliminary analysis of this problem.Item Integration of Manufacturing Resource Planning with Computer Aided Design.(1985) Harhalakis, George; ISRBy definition, Manufacturing Resource Planning (MRP II) addresses all facets of industrial business, from marketing planning through engineering to manufacturing final inspection and shipment. Computer Aided Design (CAD) is meant to assist the front end of the product life-cycle and to focus on engineering, design, and drafting-related activities. An integration of the two systems is proposed, founded on a data base level. Sample features of the integrated system include automatic part master record generation, product structure initiation and engineering change control via pictorial information. A multi-database interoperability approach is expected to develop the necessary theoretical background to support this project. The definition of a language to specify update dependencies and the communications protocol will be the means to implement the proposed integration. Eventually, a fast interpreter and the relational database system will provide the vehicle for this and future projects. It is estimated that a large number of companies already using or planning to use MRP II and CAD will beneflt substantially from such an integrated set which ensures a smooth and effective flow of information. Future plans include the establishment of more links between MRP II and CAM, CAT, and Computer Aided Process Planning (CAPP), all of them leading to the ultimate goal of using a single Computer Integrated Manufacturing System.Item Local Feedback Stabilization and Bifurcation Control, I.Hopf Bifurcation.(1985) Abed, Eyad H.; Fu, Jyun-Horng; ISRLocal bifurcation control problems are defined and employed in the study of the local feedback stabilization problem for nonlinear systems in critical cases. Sufficient conditions are obtained for the local stabilizability of general nonlinear systems whose linearizations have a pair of simple, nonzero imaginary eigenvalues. The conditions show, in particular, that generically these nonlinear critical systems can be stabilized locally. The analysis also yields a direct method for computing stabilizing feedback controls. Use is made of bifurcation formulae which require only a series expansion of the vector field. The results are easily applied since they do not involve preliminary state transformations, center manifold reduction, or Liapunov functions.Item Stochastic Unit Commitment Scheduling and Dispatch of Electric Power Systems.(1985) Yan, I.; Blankenehip, Gilmer L.; ISRUnit commitment, including economic dispatch, is a key component of short term operation scheduling of an electric energy system. Common industry practice is based on the use of a 'priority list' for generation scheduling and a deterministic model for power/energy demand. The priority list specifies the next unit to be started or shutdown in response to an increase or decrease in load. A common problem in the use of priority lists is that the next unit is improperly sized to meet the actual change in load. The algorithm proposed here is more accurate than the priority list method , much faster than dynamic programming which can hardly be applied to systems of more 5 machines. For a system of 41 machines, the algorithm can determine schedules in 0.1 second which is test enough for on-line control. Furthermore the total generating cost is superior to that obtained by dynamic programming successive approximations.Item Computer-Aided Heat Sink Design for Printed Wiring Boards.(1985) Pecht, Micheal; Palmer, Milton; Horan, John V.; ISRA computer-aided design (CAD) program has been developed which generates a graphical layout of a printed wiring board (PWB) showing its fundamental characteristics, automatically performs a heat sink design for conductively cooled in-line PWBs, and sets up a working data base containing generated thermal characteristics for subsequent thermal and reliability analysis. The program was designed to interface with an existing computer- aided component layout and routing routine and to be user interactive.Item Almost Sure Stability of Linear Stochastic Systems with Poisson Process Coefficients.(1985) Li, C.W.; Blankenehip, Gilmer L.; ISRWe consider the problem of determining the sample path stability of a linear stochastic differential equation with point process coefficients. Necessary and sufficient conditions are obtained which are similar in spirit to those derived by Khas'minskii and Pinsky for diffusion processes. The conditions are based on the deep theorems of Furstenburg on the asymptotic behavior of products of random matrices. Estimates on the probabilities of large deviations for stable processes are also given; together with a result on the stabilization of unstable systems by feedback controls.Item A Simple Proof of Stability on the Center Manifold for Hopf Bifurcation.(1985) Abed, Eyad H.; ISRA simple proof is presented for a well known fact about Hopf bifurcation: if the loss of an equilibrium point results in periodic solutions via Hopf bifurcation, then the stability ot these periodic solutions is determined by their stability on an associated center manifold. More precisely, it is shown that the characteristic exponent determining the stability of the periodic solutions is the same whether computed for the original systems or the system restricted to the center manifold. Attention is focused on the finite dimensional case of a one parameter family of ordinary differential equations. The proof consists of exhibiting a similarity transformation which uncovers the relationship between the linearized flow of the original system and that of its restriction to the center manifold. (This paper combines and revises papers TR-85-5 and TR-85-6; to appear in IEEE Trans. Automat. Cont.).Item Optimal Stochastic Scheduling of Systems with Poisson Noises.(1985) Li, C.W.; Blankenehip, Gilmer L.; ISRWe consider the problem of optimal stochastic scheduling for nonlinear systems with Poisson noise disturbances and a performing index including both operating costs and costs for scheduling changes. In general, the value functions of the dynamic programming, quasivariational inequalities which define the optimality conditions for such problems are not differentiable. However, we can treat them as 'viscosity solutions' as introduced by Crandall and Lions. Existence and uniqueness questions are studied from this point of view.Item Estimation of the Rate of a Doubly-Stochastic Time-Space Poisson Process.(1985) Gubner, John A.; Narayan, P.; ISRWe consider the problem of estimating the rate of a doubly- stochastic, time-space Poisson process when the observations are restricted to a region D subset of R^2. In the general case, we obtain a representation of the minimum mean-square-error (MMSE) estimate in terms of the conditional characteristic function of an underlying state process. In the case D=R^2, we extend a known result to compute the MMSE estimate explicitly. For a special form of the rate process, a well-defined integral equation is presented which defines the linear MMSE estimate of the rate.Item Integration of Computer Aided Design and Computer Aided Process Planning.(1985) Ssemakula, M.E.; ISRIn recent years, CAD/CAM systems have gained wide acceptance in industry. As experience in the use of these systems builds up, it is becoming increasingly evident that for most effective operation, they must be integrated. Process Planning, being responsible for the conversion of design speciflcation to manufacturing instructions, is essential to this integration process. Research is being conducted to enable geometric data trom a CAD database to be accessed by process planning programs for use in generating appropriate process plans for a given part. The resulting process planning data is then translated into an NC program which can be used to machine the part.Item An Optimal Scheme for Two Competing Queues with Constraints.(1985) Shwartz, A.; Makowski, Armand M.; ISRTwo types of traffic, e.g., voice and data, share a single synchronous and noisy communication channel. This situation is modeled as a system of two discrete-time queues with geometric service requirements which compete for the attention of a single server. The problem is cast as one in Markov decision theory with long-run average cost and constraint. An optimal strategy is identified that possesses a simple structure, and its implementation is discussed in terms of an adaptive algorithm that is extremely simple, recursive and easily implementable, with no prior knowledge of the actual values of the statistical parameters. The derivation of the results combines martingale arguments, results on Markov chains, O.D.E. characterization of the limit of stochastic approximations , methods from weak convergence. The ideas developed here are of independent interest , should prove useful in studying broad classes of constrained Markov decision problems.Item Two Case Studies in Optimization-Based Computer-Aided Design of Control Systems.(1985) Fan, Michael K-H.; Walrath, C.D.; Tits, A.L.; Nye, W.T.; Rimer, M.; Grant, R.; Levine, William S.; ISRThere have been many approaches proposed for the computer-aided design of control systems. The co-authors of this paper include several strong proponents of a design methodology emphasizing designer's intuition, man-machine interaction and sophisticated optimization techniques. This methodology has been implemented by our group as part of the DELIGHT.Mary.Lin system, an offshoot of Berkeley's DELIGHT systems. A logical way to test this approach to computer-aided design is to apply DELIGHT.Mary.Lin to a number of real control system design problems and see how well it performs. This paper describes just such applications to two control problems supplied by industry. In both cases, the problems had been previously solved by other techniques. Thus, we are able to compare the solution obtained with DELIGHT.Mary.Lin to solutions that are acceptable in actual practice.Item VLSI Architectures Based on the Small N Algorithms.(1985) JaJa, Joseph F.; Owens, R.M.; ISRDigital convolution and the discrete Fourier transform are basic operations whose computational requirements are of great importance in many applications. In this paper, we propose new types of VLSI architectures which are shown to be quite suitable to handle these operations. These architectures will result in fully pipelined bit-serial arrays which require no control units. Some preliminary implementations indicate a substantial speed-up gain over other existing designs.Item Systems Research Center.(1985) Baras, John S.; ISR