Recent Developments in System Dynamics Software

This paper is a short review of a conference held in Sevilla, Spain, in October 1987. Organized by the Systems Dynamic Society, it concentrated around concepts in methodology and applications of nonlinear system modelling within the framework introduced by Jay Forrester and his followers. The attitude to this approach is controversial. For example, the respective methodologies do not involve the identification of system parameters and the construction of the models from available data does not involve and may even contradict with the rigorous concepts and techniques of modern system theory. The review given here does not discuss the relevance of "System Dynamics". It merely gives some information on the topics presented at the conference in Sevilla

Epsilon Solutions and Duality in Vector Optimization

This paper is a continuation of the author's previous investigations in the theory of epsilon-solutions in convex vector optimization and serves as a theoretical background for the research of SDS in the field of multicriteria optimization. With the stress laid on duality theory, the results presented here give some insight into the problems arising when exact solutions have to be substituted by approximate ones. Just like in the scalar case, the available computational techniques frequently lead to such a situation in multicriteria optimization

Ellipsoidal Techniques: Guaranteed State Estimation

This paper gives a concise description of effective solutions to the "guaranteed" state estimation problems for dynamic systems with unknown but bounded uncertainty. It indicates a rather unconventional, rigorous theory for these problems based on the notion of evolution equations of the "funnel" type which could be further transformed -- through exact ellipsoidal approximations -- into algorithmic procedures that allow effective simulation particularly with computer graphics. The estimation problem is also interpreted as a problem of tracking a partially known system under incomplete measurements. Mathematically, the technique described in this paper is based on a theory of set-valued evolution equations with the approximation of solutions formulated in terms of set-valued calculus by ellipsoidal-valued functions

Ellipsoidal Techniques: Control Synthesis for Uncertain Systems

This paper deals with a technique of solving the problem of control synthesis under unknown but bounded disturbances that allows an algrithmization with an appropriate graphic simulation. The original theoretical solution scheme taken here comes from the theory introduced by N.N. Krasovski, from the notion of the "alternated integral" of L.S. Pontriagin and the "funnel equation" in the form given by Kurzhanski and Nikonov. The theory is used as a point of application of constructive schemes generated through ellipsoidal techniques developed by the authors. A concise exposition of the latter is the objective of this paper. A particular feature is that the ellipsoidal techniques introduced here do indicate an exact approximation of the original solutions based on set-valued calculus by solutions formulated in terms of ellipsoidal valued functions only

Ellipsoidal Techniques: The Problem of Control Synthesis

This paper introduces a technique for solving the problem of control synthesis with constraints on the controls. Although the problem is treated here for linear systems only, the synthesized system is driven by a nonlinear control strategy and is therefore generically nonlinear. Taking a scheme based on the notion of extremal aiming strategies of N.N. Krasovski, the present paper concentrates on constructive solutions generated through ellipsoidal-valued calculus and related approximation techniques for set-valued maps. Namely, the primary problem which originally requires an application of set-valued analysis is substituted by one which is based on ellipsoidal-valued functions. This yields constructive schemes applicable to algorithmic procedures and simulation with computer graphics

On Approximate Vector Optimization

The roots of current interest in the theory of approximate solutions of optimization problems lie in approximation theory and nondifferentiable optimization. In this paper an approximate saddle point theory is presented for vector valued convex optimization problems. The considerations cover different possible types of approximate optimality, including both the efficient, or Pareto-type, which is more frequently used in practical decision making applications, and the absolute, or strict type, which is more of theoretical interest. The saddle point theorems are used to study duality in the context of approximate solutions. The approach of the paper also provides for a unified view of a number of results achieved either in approximate scalar optimization or exact vector optimization

Ellipsoidal Calculus, Singular Perturbations and the State Estimation Problems for Uncertain Systems

One of the basic elements of dynamic modelling of complex systems is the linkage and synchronization of subsystems that develop in different time scales. The relevant techniques applied here are related to a singular perturbation theory for differential systems. A more complicated issue arises for uncertain systems described by differential inclusions, for which an appropriate theory is being developed. In order to make the theory constructive, some further steps are necessary. These are presented in this paper, where a computer-implementable "ellipsoidal" version is given. The results are particularly relevant to the linkage of models related to environmental, demographic and economic problems

A Dynamic Model of the Hungarian Forests

This paper details the submodel that describes the development of growing stock in the Hungarian Forest Sector Model - a case study of IIASA's Forest Sector Project. The model was originally elaborated for the Hungarian Biomass Study and concentrates on the relationships between the extension of the forest area, harvesting policies and the development of forests

System Identification. Paper Presented on IIASA's 20th Anniversary

IIASA celebrated its twentieth anniversary on May 12-13 with its fourth general conference, IIASA '92: An International Conference on the Challenges to Systems Analysis in the Nineties and Beyond. The conference focused on the relations between environment and development and on studies that integrate the methods and findings of several disciplines. The role of systems analysis, a method especially suited to taking account of the linkages between phenomena and of the hierarchical organization of the natural and social world, was also assessed, taking account of the implications this has for IIASA's research approach and activities. This paper is one of six IIASA Collaborative Papers published as part of the report on the conference, an earlier instalment of which was Science and Sustainability, published in 1992. The term "identification" came into use by economists in the late 1920s, but the general idea has existed at least as long as the use of mathematics in science, and is applicable to natural as well as social phenomena. Identification is finding the underlying structure that generated the observed data. In fact we never find the structure itself, but at best a model that is uniquely capable of doing what the structure does. Usually identification is sought by solving for the values of parameters in a given set of equations -- often linear equations. Professor Deistler would broaden the search beyond finding the right coefficients in a set of linear equations; his method permits the use of intuition as well as fitting to find the most likely model