This paper describes the design and application of a System Dynamics Model in simulating the future of an Engineering Company. The stress has been given in this paper to explain the application of System Dynamics principles in designing long range policies of the company. The Model is being used by the company in testing various strategies to be adopted by the management related to new projects for expansions and modernisation by simulating the impact of these strategic decisions on the objective variable. The Model assists the management in designing their long range policies to achieve the corporate objectives.
During the last five years a system dynamics model of the dental health care system of the Netherlands has been developed.The model consists of six submodels, capturing the major demographica1, pathological, psychological, sociological and economical processes of supply and demand of dental care. Two income-categories differentiating between two classes of insurance ("Sickfund” and “Non-Sickfund”), and six age-categories are distinguished. The model comprises ten types of dental treatments. Alternative policies with respect to restoring the lost equilibrium between supply and demand of dental care are tried out, and compared with the base-run. Dependent on the considered time-horizon, and the interests of different parties (dentists, dental students, dental hygienists), different policy-scenario's turn out to be more attractive in redressing the balance.
This paper uses a dynamic model to study the effect of distant and home water fishing on the Atlantic salmon fisheries. Under open access, capacity in each fishery oscillates due to overfishing and adjustment lags in capital investment. It is shown that development of a feeding ground fishery imposes significant costs on home water fisheries. In a regulated environment, joint operation of the two fisheries can result in higher total catches and profits than when a moratorium is placed on feeding ground fishing.
Despite the power of our framework as a tool for learning, system dynamics has yet to penetrate into the economics discipline. A different approach to dissemination of system dynamics into the microeconomics mainstream is presented. In contrast with the traditional product-focused strategy, the new approach uses microeconomic theory as a context for the development of student modeling skills. The approach relies heavily on the STELLA software. It is embodied in a book for introductory and intermediate microeconomics students. The general specifications and design of the approach are presented. To illustrate the approach, a sample laboratory session from the book is provided.
In The Nerves of Government (1963), Karl W. Deutsch postulated the crucial problems of "steering" and of the "creative intelligence function" - the ability to invent and carry out fundamentally new policies to meet new conditions, the ability to combine items of information into new patterns so as to find and recognize relevant new solutions - that increasingly confront government institutions and that constitute an essential aspect of the decision- and policy-making processes on which the political system may depend. This paper is an initial effort to conceive a System Dynamics (S/D) model of the U.S. Congressional system from this perspective, to promote further investigation of Deutsch's work in this area, and thus to effect appropriate change in Congressional institutional structure and function in this respect.
One constraint on the growth of System Dynamics as a methodology can be removed by enabling non-professional users to make use of System Dynamics models with reduced professional involvement. Such use requires that models be disseminated in packaged form, that is, with supplementary software that gives English-language access to the model, guides the user in its intelligent use, and performs automatic analysis of simulation results. A new generation of the DYNAMO simulation language contains tools that assist the model builder in the packaging process. Experience has shown that while the benefits of packaging are considerable, it is easy to underestimate the effort involved.
This paper describes a model of a prototypical developing nation. The purpose of the model is to understand why violence and violent repression are so pervasive in the development process. Further it is intended to show how violence affects and is affected by other aspects of development. The model, which is programmed in micro dynamo, has three sectors, POPULATION, ECONOMY, AND GOVERNMENT. Preliminary results show that fluctuations in economic growth can lead to outbreaks of violence and deteriorating economic performance.
A revolutionary new piece of software called STELLA is introduced. STELLA-which stands for Structural Thinking, Experiential Learning Laboratory with Animation -- is a system dynamics "expert system," embodying expertise in the areas of computational and structural logic, conceptualization, equation formulation and model analysis. STELLA is designed to facilitate efforts to bring the system dynamics framework to a much broader audience. The software enables even those lacking computer experience or a quantitative orientation to conceptualize, construct and analyze high-quality system dynamics models, while accelerating the development of an intuition for dynamics. Several STELLA-based products targeted at audiences in both formal education and business are described.
The past offers few guidelines for forecasting the future of a drug in a new therapeutic category, but a systems dynamics model that counts patients instead of prescriptions can help predict demand for the product.
This paper attempts to explain the pervasive problems of poverty and hunger of the developing countries in terms of the internal tendencies of their socicio-technical organization. The analysis is based on a generic system dynamics model of an agrarian economy which determines income distribution and food adequacy endogeneously but treats government policy as exogenous. It is suggested that the policies such as agricultural development, financial and technical assistance for the poor, and population control, that directly address the symptoms of the problems of poverty and hunger, may be defeated in the long run since socio- technical arrangements of the system favor persistence of poverty and vulnerability to food shortage. These policies will, however, be successful if concomitant efforts are also made to reduce income inequality through fiscal measures and to build up a food slack in the system through obtaining food calories uneconomically from cereal production.
The general considerations for the development and customization of a generic system dynamics model for rural community development are presented. A preliminary version of a generic model is presented. Alternative customization strategies based on problem complexity as perceived by the community are discussed. The customization involves generating a network representation of the problem using a modified version of interpretive structural modeling and a pattern transfer procedure to enhance the generic model. The entire procedure is based on cognitive criteria to overcome human information processing limitations; to provide a rational and systematic approach to the simplification of problem complexity, and to promote a shared understanding of the problem situation among the participants.
This paper discusses the development of cognitive criteria for use in guiding the problem definition phase of System Dynamics modeling. The System Dynamics modeling process is presented as currently defined in the literature. The problem definition phase of the process is then isolated because of its overriding influence on model structure. Topics relating to information, information processing and group decision making are discussed and the shortcomings of human judgment and inference are identified. These shortcomings are related back to the tasks required for problem definition and criteria are identified which can serve as guidelines for the development of cognitive aids for structuring System Dynamics models. The paper closes with a brief discussion on operationalizing the concepts of cognition, creativity and social interaction as tests of the relative value of these criteria.
The present article describes an example of the application of the MDS approach (Modelli Dinamici per Strategie - Dynamic Models for Strategies) to the study of criteria for a supply policy and for a consequent economic evaluation of the different supply policies which may be adopted. The aim of the study is limited to an evaluation of the direct economic effects of the different hypothetical policies, excluding those associated with the market and with different production steps. The results of a series of simulations using the model are presented along with an outline of the economic benefits deriving from the adoption of a "tight-rein" stocks policy carrying a reasonable level of risk.
This short paper is intended to stimulate thinking and hopefully more serious efforts toward understanding how systems thinking tools can most effectively catalyze the development of management intuition. This effort draws from an on-going research program, the program in Systems Thinking and the New Management Style, aimed at advancing systems thinking as a practical tool for developing a more wholistic, long-term, and creative (as opposed to reactive) orientation in organizational leadership. The program involves a network of organizations, many of which have been pioneers in developing more visionary nonauthoritarian work environments. The organizations serve as laboratories to explore innovations in management education. The central premise in these explorations is that the localization of management responsibility will require transforming an organization's capacity to learn, so that local control and understanding can advance together. The research at M.I.T. is focused on developing a library of "generic structures," relatively simple models of organizational dynamics that recur in diverse settings, which can provide a foundation for that education. This paper discusses basic assumptions about learning that underlie the program.
The failure rate for small businesses is extremely high. Inadequate financial control is a major contributory factor. The pattern of interactions between a fluctuating sales rate and the levels of receivables, payables, inventory and cash is highly complex. A model is described which simulates the experience of a small business in managing current assets and liabilities. It demonstrates the way in which liquidity changes over the operating cycle, how cash flow, and profit are dynamically different and how the firm's need for financing is constantly varying. System Dynamics is a useful tool for understanding and improving the financial management of small firms.
The law of the conservation of energy has great practical importance in physics. Is a similar law applicable to economics? For an answer, System Dynamic-related methods were applied to the economic Two Sector Diagram. They show the forces of Supply and Demand operating on the economic flows of money, goods and labor. The demand can be expressed quantitatively by a utility function, which shows that economic forces and flows are informational concepts. Consequently, the two main forms of energy in any economic system are code transport and numerical code values. Only the latter are essential.
This work is the application of systems simulation to regional analysis and its constains the philosophy and approach of the report dealing with economic growth in the Susquehanna River Basin prepared by Battelle Memorial Institut-Columbus Labs but a new look: the subsystem Input-Output matrix into the framework and with the demands (usually exogenous variables) like endogenous and with no necessarily fixed technical and capital coefficients over the time and its resolved by no conventional methods The application was in the Istmo De Tehuantepec, México.
Production of pig iron in a blast furnace is a complex phenomenon. This paper identifies the major interdependencies forming a feed back structure, leading to a system dynamic model of blast furnace. The model has been used to evaluate projects on an overall and long range basis.
Increasingly, citizens and policymakers are faced with the results of computer models and must make judgments about the model's relevance and validity. How can such decisions be made in an intelligent and informed manner? Can modeling be made accessible to the ordinary person or will it remain the special magic of a technical priesthood? This paper offers tentative answers to these questions. It first highlights the characteristics and capabilities of computer models such as are used in foresight and policy analysis. The advantages and disadvantages, uses and misuses of formal models are presented. What are the fundamental assumptions of the major modeling techniques? How appropriate are these techniques for foresight activities? What are the crucial questions a model user or model consumer should ask when evaluating the appropriateness and validity of a model? The paper is designed to help model consumers peek inside these computerized black boxes.
The economic crisis of the 1980s has revived interest in the economic long wave or Kondratiev cycle. This paper describes a simulation game which demonstrates how long waves can arise. The game vividly shows how the investment and production policies pursued by individual firms, though rational from the point of view of the individual actors, interact in the context of the whole system to produce "irrational" behavior--periodic over and under-expansion of the economy. The game illustrates te theory of capital self-ordering developed in the System Dynamics National Model Project. The paper describes the structure and rules of the game, including protocols for operating the game. The game can be played manually or on personal computers. The paper includes virtually all the materials needed to play the game, in either the board version or the personal computer version. The game board, record sheet, and a listing of the computer program (in BASIC and suitable for IBM PCs) are included.
Estimates of petroleum and natura1 gas resources vary substantially, both over time and across estimation methods. This paper develops a simulation model of global oil resources to evaluate different resource estimation techniques. Protocols for the Hubbert life cycle and USGS geologic analogy methods are developed and applied to synthetic data generated by the model. It is shown that the Hubbert method can generate an accurate estimate as early as twenty years before the peak of global production, but the geologic analogy approach overestimates the true resource base over the life cycle of the resource. The results show the applicability of simulation and the synthetic data approach to the problem of evaluating forecasting methods.
The relationship between system dynamics (SD) .and other research areas is a subject of universal interest. Attention of the paper is to the possible links between SD and GERT (short for Graphical Evaluation and Review Technique). A new simulating design for a class of GERT network is proposed and the equivalence of GERT networks to SD models established, thus a new solution to the network obtained. According to the approach, a GERT network is converted into a SD model in which levels are used to model the random variables associated with the network, such as the expected time to realize a node and the probability that it is realized. The resulting basic model can be used for calculations of any parameter of interest in the analysis of GERT networks. Its advantages and implications are discussed.
The question as to how sensitive a System Dynamics Model is to combination parameter changes in general is a complex one. A recent technique due to J.W. Hearne enables one to find the combination of parameter changes to which the system is most sensitive. The technique is applied here to an ecological model and a perturbation of the system along the most sensitive direction in parameter space is compared with single parameter perturbations of the same magnitude. The method may be useful in population control.
STELLA is a new software program that has been designed to bring system dynamics to broad-based audiences. A series of books is being developed to disseminate STELLA and system dynamics into one of these broad-based groups -- the college educational market. The books center on a "learning laboratory" approach to learning. This approach uses STELLA as the basis for an experiential, learner-controlled learning process. One of these books, "Learning Laboratories In: Physics," is described in this paper. The book contains three sections: mechanics, thermodynamics and electromagnetism. Within each section are five to six lab sessions. The lab sessions progress from simple structural models of fundamental concepts to more complex models that integrate the work from the previous labs. A sample session on Newton's laws is presented to illustrate the approach.
The purpose of this paper is to identify the main important variables and quantities which interact with the accumulation and accumulation rate, and then to analyze the intrinsic relations among them which are important in accumulation rate decisionmaking. Especially we concentrate on the relations among the accumulation rate and energy, total consumption and effectiveness of accumulation.
In this article, we analyze the tendency of technological development and the possibility to catch up with the advanced level in China. The technology progress has been playing an important part in the future, in turn, the economic growth has significant influence on technology level. According to the policy test results, we give the proposal and get the conclusions about developing technology in China.
This paper tries first to put some key factors together in an integrated system (The System Dynamics· Socio-Economic Model of China), and then reveals the dynamics of stimulations and obstructions. The stimulation results of the model show that the stimulation function of different factor changes with time, and at different times, different stimuli will be the leading factors. Overpopulation, shortage in energy supply, transportation backlog, and severe pollution are all serious problems troubling China currently and in the future. The paper also studies some possible ways to remove those barriers.
System Dynamics modeling is used as an instructional aid for the teaching of production and inventory management techniques. The roles of Material Requirements Planning (MRP) and just-in-time (JIT) systems in production and inventory management are presented and discussed. By modeling these manufacturing systems, the student can acquire an appreciation of the dynamic relationships between the elements of each system. Some elements of the Dynamo models of these systems are presented. The future opportunities and research needs are discussed.
The control policies of a dynamic system are manifest in the rates of change of state variables or levels. Irregular variation in a control will introduce random delay of the flow into the related level. Of particular interest are exogenous rapid disturbances to the rate constants of feedback loops. These disturbances lead to small random delays which build up as the system develops in time. A statistical description of this process can be obtained for a simple feedback loop as a function of the spectrum of the time series of exogenous disturbances. An understanding of this behaviour is useful for modelling stochastic systems.
The purpose of this paper is to describe a proposed framework for policy analysis and design in complex systems based on the transfer to such systems of control modules developed for simplier and more easily quantified systems. The framework is demonstrated by outlining the development of a dynamic allocation algorithm within a system dynamics model of an engineering system and describing its application in a much larger scale amanagement system. A generalised form of the algorithm is presented based on this experience which serves to highlight its isomorphic qualities. It is suggested that this framework provides an integrated approach to structural policy analysis in complex systems which can also be used to generate significant insights and perspectives into both the physical and control structure systems.
This paper is based on the premise that there is a need to formalise the procedures used in system dynamics. outside the area of computer simulation analysis, to create a stepwise procedure for systemic analysis. This need arises within the subject when applications encroach on areas where quantification is difficult or unacceptable or when a full qualified analysis is not an economic proposition or limited by time factors. The paper suggests that qualitative system dynamics should be propogated through the medium of a general framework for system enquiry. The need for general systemic methodologies is examined and the major elements of system dynamics are used to formulate the basis of such a methodology. This formulation presents a means for qualitative problem analysis in terms of the organisational structure and process control structure of systems using generally proven results developed from quantitative system dynamics models.
Northwest will be a strategically key region for the economic: development of China in the early next century. The Macro-soeioeconomic Model-·SD for a northwestern province (abbreviated to MASEM-SD) has been built. The main purpose of the model is to research into the internal and external conditions and the proper policies which are necessary to realize the great goal in 2000 set by the People's Government of the province. The model further exhibits prospects for the province in the next century and put forth some potential problems that should be paid attention to.
This article describes a tool called KBSIM and its use in model preprocessing. KBSIM consists of a knowledge acquisition system and a systems knowledge modeler which translate the responses of human tutors into structural models and facts housed in a system knowledge base. KBSIM accesses and manipulates the knowledge base through an iterrogation engine to produce information on the structure and function of a described system. KBSIM's knowledge base is a hierarchical set of matrix mapped structural models of a system to an expert level of detail. The tool is useful in integrations and strategic management, technology selection and systems modeling and analysis.
This paper tries to develop a simulation model for managing the parking systems for the city of Kaohsiung . The system dynamics methodology is employed to formulate the model. The causal structure is compartmented into five sectors: (1) the urban activity/travel sector, (2) the modal split sector, (3) the parking sector, which comprises parking supply and parking demand subsystems for both curb and off-street parkings, (4) the traffic/parking interaction sector, and (5) the financial management sector, which attempts to develop causal links between the revenue sources and expenses of the parking system. The model provides the city administrators a policy lab for parking systems management.
A field study carried out during the last seven years on a wintering population of Common Cranes (Grus grus) in Spain allowed us to gather accurate field data on-certain relevant demographic parameters: (a) the size of the Western Palearctic population of this species is estimated to be around 40000 birds, and (b) the age composition in autumn is estimated for 1979-85 to be around 13.5% young. These data enabled us to develop and test a population dynamics model which combines the density- and age-dependent effects on productivity and survival rates. The parameters of the productivity and survival functions were varied within biologically reasonable limits. From the series of possible combinations we selected those that fitted our field data on population size and age structure best. Each variable was then varied to study their influence on the model.
The United States Occupational Safety and Health Administration (OSHA) regulates the level of occupational safety and health within firms and inspects firms for violations of its regulations. Regression-based evaluations of occupational health and safety conditions in the United States generally conclude that OSHA's regulation fails to increase either the level of safety or safety-related investment. However, case studies and other forms of qualitative research suggest that regulation does increase both. Resolving this discrepancy requires a research strategy that combines elements of qualitative research and quantitative research. Simulation modelling can be used to bridge these two methods. Generally, the research project constructs a simulation model of accident generation within firms, generates synthetic data from variations of the model, and evaluates the sensitivity of regression methods to variations in the model. This paper presents the structure and base run behavior of the model used in this research project.
The analysis of the evolution of non linear dynamical systems is a complex task. The cases where: i) the model equations can be regarded as a careful and reliable representation of the real system and, therefore, need no revision or modification; ii) the parameter values are precisely known; iii) the initial conditions are precisely known, are rather rare. At least one of the previous conditions is not fulfilled in most of the systems of interest for System Dynamicists. Therefore qualitative analysis of dynamical systems, i.e. the study and classification of their asymptotic behaviours, is of extreme importance, at least in long term models.The methodologies of knowledge representation recently developed in the field of expert systems can be applied to this problem. We therefore developed MAPS, an expert advisor for the qualitative analysis of dynamical systems. MAPS takes the system equations as input, classifies them according to their features and performs the necessary calculations at each stage, sending appropriate messages to the modelist. At present MAPS deals with autonomous second order systems of ordinary differential equations. Further developments are foreseen concerning the study of higher order sytems and the design of an "equations database" for comparison with previously analyzed equations.
A new approach to Environmental Impact Assessment (EIA), based on system dynamics concepts is presented in this paper. System dynamics models will however be useful in EIA only if people are able to develop"good" models. The conceptual basis for building an expert system designed to guide people in developing system dynamics models is introduced in this work. Such an expert system will have two main modules: a system dynamics component, which will include basic system dynamics concepts and heuristics; and a specific application component, which will consist of the main relations and rules governing a givenenvironmental area. The system will also include an interface with a dynamic simulation language and with a decision aiding formulation.
This study uses a system dynamics model to understand the process of economic growth in the oil dependent economy of Indonesia. Many long-run growth patterns resulting from the various intuitively appealing development policies are analysed and an attempt is made to identify the best policy set for attaining a sustainable growth pattern. The study shows that influencing factor prices in a way to facilitate adoption of capital intensive technologies increases acceleration of growth and is a key policy to sustain growth in the long run.
In this paper, the dominant approach to the modelling of physical systems is described: it uses local laws and powerful numerical tools. For linear problems, it leads to eigenvalues and eigenvectors, in a suitable functional space, from which it is possible to construct the response to any excitation using the Green's resolvant. This approach has led to important progress in engineering physics. Nevertheless, a systemic approach is useful in physics and irreplaceable for living systems. This second way uses global laws of the phenomenon in addition with a dynamical identification of the system using some adequate experiments. We illustrate this method on the modelling of a solar plant, which is correctly represented by a simple ordinary differential equation.
System Dynamics has proven to be a useful paradigm for the construction of a policy analysis model in support of energy conservation decisions in the United States Pacific Northwest. This paper outlines the most important complexities faced by the Bonneville Power Administration planners, how system dynamics has provided a framework for analysis and how the integrated model currently used by staff members (the Conservation Policy Analysis Model) has been applied successfully to a wide range of problems.
System Dynamics Research and Consult has been asked bythe Ministry of Justice in The Netherlands to develop a simulation model of the criminal justice system. In this system a number of feedback mechanism are present that have negative side effects on the society. The first steps in the development of the model were taken. A number of small models of parts of the system were made to gain insight in the behaviour of some variables that are hard to quantify. A larger semi-dynamic model was developed to study the behaviour of the variables that are better to quantify. All models have to be integrated in the next part of the project in order to refine the forecasts.
The Dutch public authorities are confronted with large backlogs in processing the archives of their services. In view of this, the Ministry of the Interior, which is responsible for coordination of these processing activities, wanted to have a planning model for simulation, in a quantitative sense, of the archives movements within the public administration. The underlying thought was that such a model would enable problems in the fields of depot space, cost structure, allocation expertise and processing speed to be approached in a more adequate manner. A first exploration of the problem area (October 1984 - April 1985) showed that the quantitative problem of the processing backlogs is to a great extent affected by qualitative processes within the records management system and between said system and the client system. It was concluded that a planning model focused on quantitative factors cannot make an effective contribution towards solving the problems as the effects of measures aimed solely at efficiency will in the long run be affected adversely by qualitative processes. When the study was continued (September 1985 – April 1986), it was therefore decided to further investigate the processes of a more qualitative nature and to analyse their coherence. The results obtained provide a first step towards development of a simulation model for the records management system which, while supporting the relevant policies in this field, forms a tool for determining the, effects of policy changes in the system both in the short and in the long run.
This paper examines the causes and effects that interact to determine the rate the causes and effects that of Systems Dynamics diffusion. The use of Systems Dynamics implies both a way of conceptualizing the models of existing systems and the use of such models to gain a better understanding of the systems' behaviour.Given the high potential of Systems Dynamics to aid in understanding a very wide variety of systems in many areas of human endeavour the Systems Dynamics practitioners worry regularly about its slow propagation and frequently express anxiety about the future of the field. They tend to forget, however, that the potential usefulness of their approach is obvious to them but is hard to appreciate by the would be users and eventual beneficiaries of the improved solutions derived from applications of their expertise.This paper focuses on the causes and effects that in the authors' opinion interact in the diffusion of Systems Dynamics and suggests actions that may eventually help to accelerate the process of its broad adoption.
The main purpose of this work is to study the role of the women in different levels of business management. The system under study is composed of: a)business sector, in which women carry out their activities, b) educational subsystem, which provides them with the necessary skills to ascend to different managerial positions, c) cultural and socioeconomic conditions of the country, which influence : the motivation of women for this kind of work, the entrepreneurial attitude to hiring females in firms.The characteristics of the system together with the pursued objective bring us to the choice of System Dynamics as the most adequate method for our study. Using as our starting point a causal diagram of the global system, we have divided it in sectors. These represent the different aspects above mentioned. This is a long-term project from which we hope to obtain partial results to be presented in the 1986 System Dynamics Conference.
In the evolving terminology within the field of system dynamics, a "molecule" is the smallest combination of structural elements ("particles" and "atoms") necessary to represent a basic systems concept. A generic structure is the next largest combination of particles, atoms and molecules that conveys the most (or a) general form in which that concept can be identified in and/or represented for real systems. This paper proposes both a molecule and a generic structure for synergy.
The principal objetive of this study is to determine the production trend until 1995, taking into account the future behaviour of the variables which are involved in the explanation of the home market demand as well as exports of footwear. The forecasts have been made using a prospective model. By prospective is meant the effort involved to imagine the different futures which may be caused by the behaviour of the "actors" within the logial limits of the systems through which they act. In this paper a distinction is made between the variables whose dynamics are almost always constant and those which may be affected by the decision of the 'actors' or by unforesceable events. The prospective study seeks to understand the plans which the actos will try to carry out and will affect its future behaviours.These options become especially clear in the construction of partial or complete scenario. Scenario, according to the definition of Fontela (1980) is the script of a theatrical work about the future in which economic and social agents would be involved. To construct a scenario for the future is a creative task in which, implicitly or explicitly, all long-term decision makers play a part.Hence to study a scenario of the development in the next decade is to analyse one of the potential futures, being fully aware of the essentia1 unpredictabi1ity of the future and of our full freedom of choise.
A new dynamic modelling methodology, SLlN, allowing for the analysis of systems defined in qualitative or quantitative terms is presented. Simulation of qualitative characteristics is performed by applying a set of logical rules which include base, tactical, strategic and structural change rules. Quantitative simulation applies traditional system dynamics concepts. To make the transition from qualitative into quantitative modes, logical rules are also used. SLIN is advantageously implemented on a very high level language such as PROLOG, as shown in this paper. To illustrate its potential applications, simple water quality models are included.
The time delay θand capital life-time βof economic system must be considered in discussing the system's dynamic behaviour. In this paper a model of economic system with time lag has been proposed to deal with time delay and life-time. The core of this model is investment decision equation, in which the transfer function has been introduced. By selecting appropriate coefficients ai and bj the desired dynamic behaviour can be obtained. The impulse response h( t)of the system is defined by using numerical solution of its characteristic equation. The numerical solutions for proportional and proportional-plus-integral control system with 60 different sets of θ &βhas been calculated. According to the calculating results we use multiple regression analysis to get the regression equation between the critical oscillation parameters (period, amplification coefficient and amplitude) and time delay & life-time. It is convenient to apply these regression equations for choosing parameters.
Inventories of finished goods are added to the static input-output model. This addition allows one to relax the assumption that production can instantaneously track incoming orders. The reformulated input-output model exhibits production-inventory cycles over a wide range of parameter constellations. The model can be used for an extensive dynamic analysis of short-term production-inventory fluctuations in different sectors of the economy. In particular, it can be utilized to understand the extent to which each sector's fluctuations are synchronized and dependent on the fluctuations in the other sectors.The cause for the potentially oscillatory behavior of the model is analyzed. It is shown that the main reason for the oscillations lies in the assumption that the actors in the model do not know why orders are issued. They cannot distinguish whether incoming orders are issued because the recipients want to adjust their inventories or whether they are issued because the recipients have changed their long-term production plans. This result points out that one dimension of a successful stabilization policy might be an improved information policy. It is suggested that an extension of the model could be used to explain the production-inventory fluctuations during business cycles and to achieve a more detailed understanding of the behavior of different sectors during such cycles.
The determination of parameters within a system dynamics model isan important part of the model development and validation process. There are, however, very few useful tools available for working on this. The primary reason for this lack of tools has been the difficulty of applying the theory that has been developed for full feedback estimation. Useful tools can be based upon heuristic application of much of the theory. Rules are outlined that allow the easy determination and application of filtering techniques that deal with the problem of unobservable variables. The attributes of these techniques are discussed in different settings. Application to an example serves to illustrate a number of the issues.
Fundamental to the practice of system dynamics is the identification of feedback. The theory of linear model analysis and model simplification provide tools for doing this in the setting of linear state space models. The application of these tools in the field of system dynamics has been very limited primarily because the tools are inaccessible and difficult to use. Many of the, difficulties can be overcome by linking the analysis more closely with the original nonlinear model. We do this first by using time plots of model variables to describe behavior and second by deriving a nonlinear feedback model that can be used to exhibit the important feedback structure. The theory for doing this is heuristic, but allows the techniques to be automatically applied with interaction only in the domain of the original nonlinear model and its simulation.
Holland is a little, crowded country with (like most nations in Europe) a high degree of unemployment. On the one hand the government tries to provide an adequate amount of industrial sites in attempting not to obstruct economic growth. On the other hand this puts a high claim on the amount of scenery still extant in our country. Therefore the council of the central province in Holland asked for an investigation about the relationship between the supply of industrial sites and the influence on the increase of employment in each part of the province. As there are six employment-office area's in this province, a partition was made in six regions. Several branches of employment have quite different effects on claims for industrial sites, so there was also a division made in three economic branches. This results in eight teen equations for many of the relationships in the same form, but with different parameters. Therefore the DYNAMO - III -language was used in model-building to take advantage of the array possibility. The final result is a computer-model comprising about fifty array-equations, which allows the calculation of the area of industrial sites in different stages of development in each region and gives the spreading of employment over the province until 1995.
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.
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.
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 ... )
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.
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.
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.
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 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.
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 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.
This paper presents the use of optimisation as a tool for policy analysis and design in system dynamics models and presents a demonstration of its use on the 'project model' developed by G. P. Richardson and A. L. Pugh III in their book "Introduction to System Dynamics Modelling with DYNAMO". The use of optimisation to design parameters, table functions and new model structure is shown to produce every significantly improved performance for this model compared to conventiona1approaches.
There are many ways to combine Expert Systems and System Dynamics. In a short overview the paper will show useful basic combinations. As an experimental project BAMBOO will be introduced. It is primarily designed to test the usefulness of descriptive knowledge processing techniques for building and using System Dynamics Models. BAMBOO holds expertise of all SD-objects and structures, their possible combinations and the behavior they cause. BAMBOO generates the necessary knowledge about the user model by a system driven dialog. On the basis of this knowledge it shows the conclusions the model implies. For instance, BAMBOO determines which variables are sensitive and how the model will propably respond during the simulation.
This paper deals with the analysis of the classical investment and pricing problem of a monopoly faced with competition from substitute industries or marginal firms in the same field. The monopoly owns a finite level of a resource (ie, the stock of an exhaustible. resource), whose usage is to be divided optimally over a finite planning horizon. The demand for the resource is described by a downward sloping demand curve which is affected by the measures of the competitor. The monopoly and its competitor are maximizing the present values of their net profits over the planning horizon. The problem is first formulated as a non-cooperative differential game. The necessary conditions for the Nash solution are derived.The necessary conditions for the solutions are stated as a two-point boundary value problem which admits also an analytical solution if some simplifying assumptions are made. However, to relax these assumptions numerical solutions are computed by employing System Dynamics.In terms of System Dynamics the two-point boundary value problems have initial states for some level variables and terminal states for some other level variables. To solve this problem with System Dynamics we have used the Newton-Raphson method. In the Newton-Raphson method two System Dynamics models are needed: one to produce a Jacobian matrix and another to produce solutions for the original problem.
Today for managers or in general for non data processing experts the use and application of simulation models is of very high expenditure. Editing and changing model parameters, studying the simulation language or applying e.g. a graphical standard software package are very unusual activities for this special user group. Due to this situation it cannot be expected that simulation models which deliver very important results for decision support get near to these people. In this paper a user friendly communication and control system is presented, which offers an optimal user guidance in modifying and running simulation models, in creating a user friendly graphical output and in the interpretation of the model results.
For a utility application in the capital goods sector use of new technology in production gave the possibility to have a new product at much lower cost than competition There were about five competitors with approximately equal market shares. In order to optimize timing of marketing and production an analysis of market and competitors' reactions was started.The work reported covers the main steps and findings of this analysis made in preparation of execution of the optimized marketing exploit.These steps cover conceptualizing of market-competitor relationship, modelling and simulation to define sensitive parameters, defining some robust market policies and analysing the operational information requirements in executing a set marketing concept. Specific results obtained were above all elimination of some crude "feel of the pants" notions how to sell and confirmation of the importance of a selling policy even in a seemingly orderly and settled market environment.Other results contributed very much to an understanding, why a new product at much lower cost is only in part able to gain market share in a setting of wary competitors.
The course of know-how transfer of multinational corporations in developing countries is presently considered to be very problematic from the view of multinational corporations as well as from the view of developing countries. This paper first develops a descriptive model of this problem. The descriptive model is based on empirical and secondary statistical investigations of Japanese, US-American and German assembling industry multinationa1 corporations (automotive industry, electrical industry and mechanical engineering industry). The descriptive model shows that the know-how transfer process is a process of structural change resulting from the interaction of multinational corporations, local corporations and developing countries. Based on this descriptive model we have developed a formal mathematical model of the evolutionary process of know-how transfer by introducing "spiral loops" as a methodological extension of the system dynamics approach. The spiral loop concept which is based on new developments in evolutionary theory and in the field of artificial intelligence is used to model the qualitative changes in interaction processes which are responsible for structural change and evolution. The feedback loop concept and the concept of shifting loop dominance are used to model quantitative changes in interaction processes. The combination of the traditional feedback loop concept of system dynamics with the spiral loop heuristic allows us to model dynamic interactive processes between two or more autonomous systems in their quantitative and qualitative dimensions. Plots from simulation runs of the model show the evolutionary pattern of the existing know-how transfer process, which is considered problematic. We have analyzed different patterns of this process with model tests in order to generate policy and strategy recommendations for managers of multinational corporations and politicians in developing. countries.
The control of new product growth and market penetration is a key task for corporate management. The concept of Decision Support Systems is applied to this field of problem solving. A general model of innovation diffusion is presented and used to study market response and profit impact of different strategies. Its analysis suggests a marketing approach which aims at rapidly gaining sales volume. Attractive prices and fast capacity built-up take effectively into account the dynamic environment.
By analyzing the dynamics of resource allocation in a generic management system, this paper illustrates how chaotic behaviour can be internally generated in a typical System Dynamics model.
A dynamic simulation model of interfuel substitution in Oecd-European electricity production is presented. A combination of a priori information and a calibration of the model to hictorical development produces several important results. Adjustment times are much longer than usually assumed, and price elasticities are much higher. Both the simulation model and econometric estimates indicate that the LOGIT model is a better representation of fuel choice in the sector than a constant elasticity function. The LOGIT model explains why estimates of price elasticities tend to vary over time. It also indicates that a fuel can price itself completely out of the market. Finally, the results indicate that coal is protected equivalent to a price subsidy of about 36 percent.
Business decisions about investments have to be guided by the careful study of market behavior. In this paper an attempt has been made to study the market behavior adopting a modular approach. The total demand of a product in a market gets influenced by a set of four major feed backs related by market saturation, capacity expansion, price fluctuations and motivational efforts. In the paper each of the feed back has been seperately discussed to arrive at a feed back structure which can be used for designing the policies related to expansion of capacity, pricing, motivational efforts etc.
The majority of women report that they have been victims of sexual harassment (Safran, 1976, Tangri, Burt & Johnson, 1982). Sexual harassment has been linked, both theoretically and empirically, to psychological and physiological stress, often accompanied by somatic symptoms such as headaches, nausea, and loss of concentration, as well as decreases in job performance and increased absenteeism and turnover. In addition, estimated losses in the federal government alone were in excess of $189 million over a two year period. This paper is one of the first to unify the past research and empirically consider sexual harassment in terms of its underlying mechanisms. It is also one of the first to examine the dynamics of the harasser and the organization in which the harassment occurred. Interactions between the victim, harasser, and organization sector are explored. Results indicate that longstanding organizational traditions of sexual harassment may make it difficult to eliminate harassment in the near future without a comprehensive group of policies concerned with eradicating sexual harassment.
Just-In-Time (JIT) production is the notion of producing the necessary products in the necessary quantities in the necessary time in every process of a factory and also among companies. It is not uncommon to find JIT used synonymously with "Kanban," which is the name for a specific inventory replenishment system developed by Toyota to accomplish JIT production. The Kanban system employs cards (kanbans) to signal both the need to deliver more parts and the need to produce more parts. A unique feature that distinguishes the kanban-based JIT system is its unique "pull" nature. The paper begins with a review of JIT production and the Kanban system. Then, using the structuring principles of System Dynamics, a simulation model of a kanban-based JIT production system is developed. The formulation effort begins with the "simple structure" of one production stage. By connecting a few of these "basic structures" and adding a market interface module, a complete multi-stage manufacturing system is developed later.To test the internal consistency of the model, several simulation experiments are conducted. The unifying theme in these experiments is the issue of flexibility: How well does the system adapt to changes. The simulations are thus designed to show, for different management policies, the behavior of the system in response to unexpected circumstances. The following cases are considered: normal response, changing the number of kanbans, a breakdown, small and large demand increases, bottlenecks, and capacity planning. Finally, the results of these simulations are used to point out some of the managerial trade-offs involved in JIT production.Although the major contribution is the conceptualization and formulation of the system dynamics model, the paper lays the groundwork for subsequent normative research in the field of operations management.
The St. Radboud Hospital of the University of Nijmegen, The Netherlands is sponsoring a System Dynamics computer simulation designed to study the hospital's textile (bed, catering, medical linen and uniforms etc.) circulation process.
Sponsored by a Dutch Roman Catholic Foundation a System Dynamics computer simulation model has been developed to study the population dynamics of priests of the Dutch Roman Catholic Church. Few vocations since the second half of the sixties led to a disproportional 'going grey' of the priest population. This is manifested not only in the unbalanced age structure but also in a relatively high number of retirements.The model (see enclosed flow diagram) structures on the one hand the physical demographic processes and on the other embodies a theory based on observation of qualitative aspects of disaggregated priest, believer and non-believer populations. Church attendence figures for instance are used as a measure of vocation potential.The model is used to articulate the insights on the influence of policy alternatives on priest population in the coming 50 years or so.
We study the problem of the adequation of the market prices to some "production prices" with which an intersectorial equalization of the gain rate was obtained in an ideal capitalism of free competition. We criticize the treatment of this problem by Marx, Sweezy and Salama-Valier, by its static or aprioristic character. And we propose a system of dynamic regulation utilizing the intersectorial coefficients of an input-output table and supposing full mobility of the capital. The study of this system permits to conclude that the equilibrium values of the gain middle rate and of the production prices depend exclusively of the intersectorial coefficients of the directly or indirectly productive sectors. From this, we study the evolution of the market prices. of the production prices, of the capital organic composition, of the gain sectorial rates and of the gain middle rate from a modification of these coefficients in an equilibrium situation.
After enduring years of criticism from prominent economists, many members of the system dynamics community have concluded that economists do not like system dynamics. This article argues that this conclusion is not entirely correct. The economics profession can be divided into two methodologically different camps: the mainstream or neoclassical economists and the institutional economists. Although neoclassical economists do not see system dynamics models as being scientific because they do not adhere to the tenents of logical empiricism, institutional economists construct models in a manner that is strikingly similar to the system dynamics method. Indeed, it is shown that system dynamics can be used to strengthen and extend the institutionalist paradigm in economics and thus has the potential to find a permanent home within the profession. The computer people took seriously the evidence that people are not maximizing-rational and decided to find out by empirical study how decisions are actually made. Thus they became, in a way, heirs of the institutionalist program ....Philosopher of Science Paul Diesing
In many of the United States, attempts to reform the funding of public education to reduce disparities among school districts have been disappointing. For this study of state aid-to-education in Connecticut, a system dynamics model of local district budgeting behavior was formulated, replicated seven times to represent all the school districts in Connecticut divided into seven clusters, and linked to a state-aid sector that dispenses aid according to the state's current guaranteed wealth formula. Simulations of a single cluster and the seven-cluster model suggest that the guaranteed wealth formula will not, by itself, narrow the gap in per-pupil expenditures in rich and poor districts, as intended. The study described is a relatively pure case of policy modeling designed not to confirm hypotheses but rather to draw inferences from puzzling sets of assumptions about state and local behavior. Reflecting on this case, we suggest six conditions that appear to indicate that a policy problem is ripe for the sort of contingent, inference-generating analysis illuminated by the Connecticut study. Some speculative methodological connections to cognitive science are also suggested."
A mathematical model and digital computer simulation of the human renal filtration controls are herein developed. The purpose of the model is to provide a method of analysing renal filtration control hypotheses which cannot easily be tested in an animal or human. The method used in the construction of the model was system dynamics.We propose an original formulation for the numerous different variables, eg, Bowman capsule pressure, glomerular absorption, net filtration and other considered variables in the model.This model can simulate the dynamic functions of variables such as colloidal osmotic pressure, glomerular capillaries, tubular filter, along with other clinical determinants.The model simulates disparate situations, such as the effects of renal filtration variations of arterial pressure, concentration of plasma proteins...The results presented coincide with those of other authors.
Systems Theory has developed without inner coordination.The General Theory has been general in the sense of trying to reach a global viewpoint from the perspectives of science and philosophy. But it has not perceived its structure as a whole. It has grown in complexity without integrating its parts.Systems Dynamics has expanded in relative isolation. It has developed into a closed methodology with fixed principles and structure. To a great extent it has been equated to the Forrester's methodology applied to industrial, urban and global systems.It would be valuable to place the Dynamic approach in a wider context. It is assumed here that in a General Systems methodological framework the same system can be considered from three different, but complementary, viewpoints: Static, Dynamic and Dialectic. It is also assumed that closeness and openess of systems are relative states and that analysis and synthesis should have analogous methodological weight.Systems Dynamics appears as a central node in a systemic methodology that should integrate different approaches and viewpoints into a coherent whole.
This paper re-examines the economic development problem and establishes that organizational arrangements underlying resource use at the social, political, and ecological levels, not shortage of resources per se, or their inefficient employment, are responsible for creating conditions of underdevelopment and for the failure of the well-intentioned economic development efforts made in the past. Three levels of national organization are examined: the social level which is concerned with the production and distribution of income among various cross-sections of society; the political level where decisions are made to allocate resources to public welfare or to maintaining control over the public; and the ecological level where a resource mix is selected for use on the basis economic and technological considerations. The analysis is based on three separate formal system dynamics models of the resource allocation processes dealing with each of the three levels of national organization discussed above. Appropriate institutional arrangements for fostering sustained national growth are explored.
The study aims to assess the potential of the forest sector to maintain its leading role in the Finnish economy. The long range future alternatives are simulated by means of a System Dynamics model called MESSU. It is shown that within the limits set by the availability of wood and the low profitability of the forest industry, the growth of total production in the forest industries cannot meet the projected increase in international demand with the present product mix. MESSU covers the whole forest sector (forestry and the forest industry), which makes it possible to study the interaction between the different parts of the sector. The model is built up of seven submodels (modules): forest, forest ownership, roundwood market, harvesting, forest industry, end product market and capital market.MESSU does not only consider economic features of the forest sector, even though they are a central part of the model. Biological (timber growth) and technical (e.g. efficiency of forest industry production and harvesting) features are also included. Further, sosio-economic issues, such as population, urbanization and labor supply dynamics, are considered.
The population of the Tokyo Metropolitan Region increased by about 3 millions in the five years between 1965 and 1970. This increase was due mainly to the flow of populations from the outer field of the Tokyo Metropolitan Region. Until around 1955, population increases were noticeable within the special wards of the metropolis. However, while there has been a recent lull in the increase rate of in-migration, there has been a remarkable increase in the amount of out-migration from the special wards to the four adjoining districts, the Tama district, Chiba Prefecture, Saitama Prefecture, and Kanagawa Prefecture. Out-migration exceeded in-migration in 1967 for the first time since the end of the War and the gap has been increasing year by year. On the other hand there has been gradual rise due to natural increase (the difference between births and deaths) in recent years, which has come to occupy a greater part of the population increase within the area of the Tokyo Metropolitan Region. Our model therefore was formulated to represent such relations between the ward area and the four adjoining districts, as migration, residential effect and commutation. We have divided the whole system into 5 sectors, corresponding to the ward area, the Tama district, Chiba Prefecture, Saitama Prefecture and Kanagawa Prefecture. Each sector is subdivided into population, residence, and enterprise sub-sectors.The simulation was run for the 150 years from 1900 to 2050 and the results contained World War II effect on the population, the number of residences and enterprises of the ward area.
The paper studies with the help of a model the employment decisions of a firm through a business cycle which maximizes its discounted income and assumes that the forecasts are perfectly corred.The firm produces a output function of number of workers employed by the firm at time t. The firm's labor force increases over time as a result of layoffs and quits. The firm can recalls workers at time t only if it has an inventory of previonsly laid off workers. The firm's output is supposed superior or equal to demand (function of price and time) at any time. The solution to the maximization problem will then yield an optimal output and employment plan which the firm proceeds to implement until its expectations about demand at time t.
A three sector system dynamics model (clams, natural predators, and baymen who harvest the clams) was developed to evaluate measures to counter the sharp decline in New York's hard clam (Mercenaria mercenaria) fishery. Six management alternatives were evaluated: effect of shellfish hatchery production on increasing the abundance of clams; growing seed clams on racks to protect them from predators; a maximum size limit on the harvesting of clams; limiting entry of baymen into the fishery; a bounty on predators; and setting aside a portion of the bay as a natural nursery. Model results, which were largely unanticipated, are described.
The decision rules in simulation models purport to describe decision-making behavior as it is and not as it should optimally be. Without the criterion of optimality to judge the appropriateness of a decision rule, simulation modelers must rely on empirical confirmation of the structure of their models. In models of small organizations, traditional social science methods may be used. But these methods are infeasible in models of larger systems such as industries or the macroeconomy. This paper shows how direct experiment can be used to confirm or disconfirm the decision rules in simulation models. Direct experiment uses interactive gaming in which human subjects play a role in the system being modeled. The subjects play the game in the same physical and institutional context assumed in the model, and are given the same information set, but are free to make decisions any way they wish. The behavior of the subject can then be directly compared against the behavior produced by the assumed decision rules of the model. An example is described in detail and the correspondence of the experiment to reality is discussed.
This paper examines the domestic energy consumption in Pakistan in the backdrop of the government's pricing policies using a system dynamics model as an explanatory tool. In the context of policy analysis, the simulated behavior of the system are tested based on various pricing schemes of the competing fuels. The simulation experiments reveal, among others, that Pakistan's energy system structure is such that any policy involving government control over the prices will eventually result in an increase in burden on family income of rural and urban poor classes mainly and urban middle class partially. It seems that the only way to redistribute the burden on family income, minimize the burden on national economy, and also achieve conservation of fuels, is by allowing the price of fuels to be determined by the supply-demand conditions of the market.
A great interest has been raised recently on chaotic behavior in system dynamics models. This interest is largely justified. The discovery that deterministic systems can show chaotic behavior has deep consequences for the system dynamicist. Among other things, it is well known that strange attractors show a pathological sensitivity to initial conditions. This property impedes the use of a single trayectory (obtained by simulation) as representative of the system behavior. So, the traditional working way of the system dynamicist should be deeply reconsidered if these strange attractors are exhibited by their models. This last is higly possible due to the nonlinear character of these models. Therefore, the system dynamicist should be able to study whether or not those attractors appear in his models. If they appear, then the classical study through the analysis of the trajectory should be rejected, and studies of an stochastic nature -not yet well understood- should be undertaken.
We propose a functional design for a software system whose aim is to provide support for an structured methodology of modelling and simulation in System Dynamics. The design follows mainly the ideas of Multifacetted Modelling developed by Zeigler. Our approach has been to give a hierarchical version of DYNAMO and a collection of functions for the handling of simulation elements in an unified system.
SDSE is a microcomputer based, interactive and integrated system designed to facilitate the teaching and use of System Dynamics in Education. In this way teachers and students without extensive Computer training are able to construct and simulate system models after short period of learning. System Dynamics has been included in Atenea, a Spanish Ministry of Education and Science project in order to introduce computers in Education. Nowadays, SDSE is being used as a supporting program to teach System Dynamics to school and high school teachers in Atenea project courses run by Comunidad Aut6noma in Murcia. In this paper, functional characteristics of the system are described, at the same time that SDSE is applied to build and simulate the simple·and classical example of the inventory control system. Nowadays, SDSE is programmed in FBASIC (FUJITSU FM/7 ) and GWBASIC ( IBM PC and compatible)
When distribution of economic goods, equipments, ... takes place among different regions, it is expected to carry out in an optimal way, considering "optimal" the way of distribution that assigns more to the neediest regions; thus, numerous factors such as economic conditions, actual equipments, social conditions, population, etc, should be taken into account. The presented model has a double aim: firstly to show the present behaviour of distribution system of investment in Comunidad Autonoma de Murcia, regionally, and secondly to get this distribution to optimize a linear function that represents the regional social welfare as a consequence of the social welfare in each region of the Community and dependent on linear constraints. To reach these objectives, a mixed model that combines both System Dynamics and Linear Programming techniques is constructed; a relation between both procedures is established in order to simulate both the natural behaviour of the distribution system and those decisions that make this distribution to be optimal. Along this report the method carried out to handle mixed models as well as the particular model MURCIA A/I are described.
This paper introduces a new implementation of the System Dynamics simulation Language DYSMAP, a current project at Salford University. A short overview of the history, syntax and features of DYSMAP will be given. The new DYSMAP2 system operates as an interpreter. The relative merits of computer interpretation vs. compilation into FORTRAN will be discussed. An outline of the operation of this new portable package (written in FORTRAN77) will include high level descriptions of the parser, run-time interpreter, the interactive environment, dimensional analyser and the optimiser. The performance of the new DYSMAP2 package will be illustrated.
In this article we want to predict the dynamic behaviour of a portfolio of assets, i.e., we want to know how quickly it will move towards anew position of equilibrium when an unstable situation has ocurred due to important changes in the risk, (and in some cases in the return) of the securities. In order to carry out this forecast, first we should locate the points of equilibrium, then analyse their stability and lastly determine where, and under what conditions, the discontinuities appear.Changes in the return or in the risk of the securities which make up a portfolio can be smooth and this also brings about a smooth change in the portfolio, which is shown in a readjustment in its composition. However, it sometimes happens that, while the expectation of return remains relatively stable, circumstances arise which considerably increase the risk, in which case a serious discontinuity occurrs in the feature of the portfolio.In this way, we can apply the methodology of Thom's Theory of Catastrophes in order to obtain valid conclusions using the morphology of the butterfly catastrophe for the portfolio's feature (efficient, non-efficient and opportunity or pseudo-efficient), employing four control factors: return, variance, transaction costs and risk aversion.
For the use of ecosystems with savage fauna it is essential to dispose of -instruments which can let one to simulate the effects that natural circumstances or human actions could have on them. Because ecosystems are extremely complicated and because we are not able to experiment "in real life" -behavior are irreversible- it becomes necessary- "to experiment in the laboratory" the effects of the different events that may affect its future life. This "laboratory tests" can be done with the construction of an ecosystem (a model is a formal representation in scale) that later will have to be implanted on a bearing, and will be the object of simulation exercices. A good procedure of the construction of the model and the simulation is what we calle “System Dynamics” (DS).The non existence of previous proofs in the use of ecosystem with savage fauna leads conscious of unconsciously to the disappearance of going down of the species in specific ecosystems. The examples of Kaibab's land, the “Urogallo cantábrico" or of the grouse -are paradigmatic. The purpose of this work is to introduce concisely the model and the conclusions obtained from its use, for the study of the evolution of the rabbit population in a plot of 10 hectares in South Spain. The rabbit (Oryctolagus cuniculus, L.) has been chosen for its enormous value as a prey for upper birds of prey (Imperial eagle, Royal kite, Black kite, Linx and Fox, etc. etc.)
Since L.V. Bertalanffy first brought forward the general system theory, people have been paying more attention to research work from the systems point of view, thus bringing about the development of some system scientific fields such as systems engineering, operations research and management science, etc. Now, in addition to general system theory, there are many new subjects related to studying system 'dynamic behaviors and self-organization such as synergetics, dissipation structure theory, etc.In this article, we study system dynamics from a philosophic viewpoint and try to study important points and methods that can be introduced by systems theory. We search into the relationships between system dynamics and other fields.
From the viewpoint of system dynamics the whole structure and functions of a system do not simply equal the algebraic sum of the parts which the system consists of. There universally exist mutual relationships between the transmition and exchange of information, energy and material within the whole system, its parts and its environment. The aim of this paper is to study the organic ties among the three of the whole, parts and environment of a system and the transmition involved under specific conditions. In this paper, the logical relationships between the internal and external parts of the system are described. Two concepts of the transmition matrix and the relationship matrix are presented along with the definitions of the grades of the grades of variables. Their concepts and definitions, combining the theory of the model reference self-compensation, are used to form a new method by which the functions of the structures and relationship between the whole system and its parts can be identified. Some satisfied results have been obtained from testing this new method on the Boom-town Dynamic Model.
This paper tries to use System Dynamics as a tool to analyze some existing problems in China's energy system. The paper first points out some most severe energy problems in China and the policies that people suggest toward the solving of these problems, then reveals the dynamics of these policies through simulations on an Energy Dynamic Model that we built. The analyses cover the issues of energy production and supply system, energy price, energy shortage, and industrial capital retrofit toward energy conservation, etc.. Some conclusions are derived from the analyses which are valuable for the solving of China's energy problems. And System Dynamics is believed to be an effective approach in energy price analysis in China.
With the rapid development and wide application of microelectronics, the electronic industry is playing an ever more important role in modern economies. Backed by the socioeconomic circumstances, a system dynamics model (SDEIC) is constructed to investigate the development of electronic industry andto give a description on the future of microelectronics in China in some way. The analyses and simulation results show that there will be a prosperous period for the development of the electronic industry in the coming twenty years with a vigorous investing requirement and at a relative high growth rate. A notable characteristic is that the development is unbalanced with electronic consumption products dominating the market in terms of volume in the period concerned.