A system dynamics model is presented which integrates current knowledge on the various aspects of normal and abnormal weight control and which provides new insights into the mechanisms underlying certain eating disorders. Anorexia nervosa, in both its purging and non-purging variants, emerges from the model as a behavior pattern tied up with the fear of weight gain which serves to strengthen the individual's drive toward extreme slimness. Policy tests suggest that appetite-suppressing drugs may be helpful in reducing this fear and its negative physical consequences. The encouragement or discouragement of physical activity may also serve the goal of stabilizing the individual, depending on how different therapeutic objectives are weighted for the specific individual. Future research may take the form of model enhancement or of empirical studies guided by the model's structure and behavior.
DYNAMO has been used for many years on mainframe computers. Like many other applications programs and computer languages, it has been made available on Personal Computers. Will that make System Dynamics easily available to many potential users who never tried to use it on mainframes? Does one need to be an Information System specialist to use DYNMO on a PC? These are the questions to which this paper intents to give an answer to. Subsequently, we used DYNAMO on a PC for a very simple financial application, and compared it superficially with the (already) traditional approach of spreadsheets.
A process modeling approach is used to describe three major elements of policy making, namely, the workings of the corporate ,system of a firm, its representation in Managers' Cause Maps, and the Policy Formation Procedures used by the policy making elite. System Dynamics provides an expert system to aid the construction of the Corporate System. Cause Map and Behavioral Decision Making theory, on the other hand, provides the artificial intelligence (modeling the collective decision making behavior of a senior management) that drives the Corporate System. Potential applications of the methodology are put forward.
In this paper an Expert Aid for System Dynamics Modelling (EASDM) is introduced, a user friendly, interactive software tool which helps users unfamiliar with System Dynamics and computers, to construct their models from the formulation to the simulation. The most important feature that distinguishes this aid from its closest predecessor (ASDM) is the incorporation of an expert system capable of carrying out the conversion from the causal diagram to the Forrester schematics in a semiautomatic way. This is possible because, within the context of the causal diagram, there is an implicit set of "rules" which allows the classification of quantities. EASDM has been programmed in PROLOG and Pascal for personal computers with the MS-DOS operating system.
A non-lineal mathematical model of capillary dynamic has been constructed to study the reanimation stage and the effect that different treatments have on burn patients. This analysis allows a qualitative and quantitative knowledge of the dynamic behaviour of variables very difficult to quantify in daily practice, like plasma volume, net liquid shift in burned and non-burned areas, etc.The value and fidelity of the model was obtained by comparison of the reckoned results with those measured in a serie of patients of the Burn Unit of a General Hospital.
A system dynamics model reflecting the structure of the interaction between the .two languages operating in the Basque Country has been built. People have been classified into three different groups depending on their knowledge of the language. These groups of population are subjected to a normal demographic evolution and to a linguistic interaction. The interaction among the populations is controlled by two major levels: the basque culture and the development factors of the language. The only exogenous input to the model are political actions to raise or to decrease the development factors level. Although the model proves to be sensitive to these actions a delay time of about sixty years is to be expected in the response of the population.
Our purpose is to set up a dialogue, a scientific exchange, between CIRCULATORY ANALYSIS and SYSTEMS DYNAMICS, since we belive the two -disciplines to be complementary. In fact, we would go so far as to say that S.D. represents the natural development of C.A. We consider there are well-founded reasons to expect the cooperation between the two disciplines to be profitable in helping to subdue the system of economic circulation and to subject it to a rational control.Circulatory Analysis can offer Systems Dynamics the conceptual riguorousness of a theory of circulatory systems developed from solid bases, and even some new concepts which may be very useful (for instance, those of Circulatory Process and Complex Circulation). On the other hand, Systems Dynamics can offer all its engineering capacity to produce working models. In order to show more clearly what Circulatory Analysis is, we have made a small toy, a model constructed to simulate the behavior of the system of economic circulation in a commercial business. It is extremely simple (it is, after all, a toy), but the same methodology used for its design and construction can make it possible to produce machines, that is, simulator models, to any degree of complexity.
This paper presents a Continuous Simulation Software (LSC) developped in our laboratory. The first version of this software treats dynamical systems , that are described by a set of explicit linear or non linear algebro-differential equations .The software has an interface (High Level Language), that permits an auto-guided dialogue with the user. The internal architecture of the system is structured in two subsystems: a control subsystem and an operating subsystem The package contains a library of algorithms and external functions that permits simulation models from different fields (socio-economic, technological ... )
The power and utility of system dynamics depends on going beyond a model to implications and generalizations that can be drawn from the process of modeling. System dynamics papers too often stop with the description of a model. But to be effective, models should become part of a more persuasive communications process that interacts with people's mental models, creates new insights, and unifies knowledge. In doing so, modeling can make use of the full range of available information--the mental data base and the written data base, as well as the numerical data base. The last century has been devoted to exploring the frontier of physical science. During the next century the great frontier will be exploring the dynamic nature of social and economic systems.
The analysis of the causal structure of economic models is a tool for understanding the functioning of existing models, particularly in their interdependent component, and also for assisting the modelors in the process of constructing or modifying large econometric models. In this paper the authors briefly describe the methods of causal analysis and apply them to the Wharton-UAM model of the Spanish Economy. The paper, in English, discusses suggested modifications of the model as a result of the structural analysis and is completed by two Appendices, in Spanish, discussing the theoretical construct of the model and the detailed results of the causal analysis; in an Annex are also reproduced the variables and the equations of the model thus introducing the reader to a fully documented version of the model.