Several interactive computer graphics technologies are now available that can provide powerful tools which enhance our ability to conceptualize, implement, and communicate complicated system dynamics model structure and behavior thereby giving us opportunities to improve our effectiveness as researchers, consultants and educators. This paper gives an overview of several projects utilizing interactive computer graphics and evaluates their significance for system dynamics. Included in this discussion are: 1) computer aided design systems for “automagic” design and updating of overview, policy structure, flow, and causal loop diagrams, 2) computer teaching games and self-paced interactive computer aided instruction packages designed for personal computers; 3) review of the new Micro-DYNAMO and Hewlett-Packard plotting software from Pugh-Roberts, 4) computer networks, computer conference based academic programs for the general public, and network indexed video cassette extension libraries of system dynamics presentations and seminars; 5) interactive computer driven video disk processors with touch sensitive screens allowing a modeller multimodal access to overview, subsystem, policy-structure, causal loop and flow diagrams, table functions, documentors, and DYNAMO equations on the same system; and 6) two- and three- dimensional representations and animations of model behavior on multicolor dynamic displays driven by computer and video disks. These developments are assessed with respect to their possible contribution to the growth of system dynamics as a field, dissemination of system dynamics methodologies and to the implementation of policy recommendations. Because of falling prices for software and hardware, the explosion in interest in personal computers, the exponential growth in their functionality, and the current state of the field, we believe the next two decades will be the phase of most rapid growth for system dynamics.
A number of challenges face firms that need to decide when and whether to convert from technologies to new computer-based technologies. Such is the case with lithographic setup shops, which prepare photos for color printing; they must choose between continuing with traditional craft methods or acquiring digital image-processing equipment. Pioneering firms can be saddled with experimental, undependable, and expensive prototype systems. Rapid technological changes still occurring in digital systems can allow competitors who invest later to obtain cheaper, more effective equipment. But firms investing later may find themselves paying for the large investment just when most competitors are established in the new technology and competition has forced prices and profits to low levels.In order to create an organizing framework for analyzing and developing conversion strategies for these firms, we worked in collaboration with Inter/Consult, the project's sponsor, to build a system dynamics model of the color process industry, its market, and a typical firm. The primary purpose of the moel is to provide a clear understanding of the impact these major capital investments will have on the profit structure of lithographic setup shops and to help these shops develop effective conversion strategies. A secondary purpose of the model is to aid digital image-processing equipment suppliers in understanding their market and to provide them with a toll for generating alternative scenarios given different assumptions about economic trends, technological developments, prices, market size and composition. The model serves as a strategy support system that allows clients to derive scenarios explicitly from causal assumptions and to evaluate alternative investment strategies.
An experimental software package is being used as an extension to the DYNAMO IV compiler to linearize the model at any point during a simulation, compute the eigenvalues and eigenvectors of the linearized system, identify the levels important in producing each behavior mode, and compute the elasticity of a given eigenvalue (corresponding to elasticiy of period and damping) with respect to all model parameters. The package is intended to help modelers understand the causes of behavior in very complex models, both for debugging implausible behavior, and for presenting the causes of plausible behavior more convincingly. The package is able to work for the System Dynamics National Model, a model of around 300 levels. Practical experience has uncovered some difficulties in making the analysis useful,, but these are being surmounted. The experience suggests that mathematical methods should be used extensively “in the field” before being offered as candidates for expanding the paradigm of System Dynamics modeling.
For four years, the authers have been studying agricultural products markets with this year a development on lumber market. Search goals are not only to understand market working processes but also to define for each of then the M.I.S. necessary to permit some control by interprofessional organisations specially on price levels. The paper presents in a first step two building model approaches: One is a pragmatic approach, formalised by Buffa, Cuzo, Bonini, Boulden, Cetenick, Rosenzweig, on San Diego meeting, A.M.A., in 1970, the other is a theoretical approach by Bross, Schoderbeck, New -York in 1971, and Kaplan, Scranton in 1964. In a second type, the use of System Dynamics approach is confronted with these two first methods specially on noted research area, In conclusion, results of our models are discussed.
This paper uses a system dynamics simulation methodology to assess the potential effects of new accounting policies being considered by rule formulating bodies. The key objective of this paper is to demonstrate that current ex-ante intuitive assessment of the effect of proposed accounting rules is inadequate due to the counterintuitive nature of economic consequences in a complex social system. For this purpose a very simplified model of he US economy is developed and its parameters varied to reflect potential accounting policy changes. The effects of these policy changes are shown to be counterintuitive in nature, requiring consideration of second and third harmonics of the feedback loops for adequate ex-ante impact assessment. This paper is divided into six parts: the first part describes alternate approaches to economic consequence assessment and the advantages and disadvantages of utilizing the system dynamics methodology; the second part describes the skeleton of the system dynamics model; the third part examines the measurement problems of rates, levels, and delays as well as reviews the details of their computation for model formulation; the fourth part discusses the problems and results of model validation efforts; the fifth part describes some of the results obtained from application of the model, and their meaning in comparison with traditional methodologies for accounting impact analysis; the sixth part concludes by suggesting the next step for macro-accounting modeling: evaluating the potential and shortcomings of this methodology.
:One of the traditional obstacles to effective utilization of simulation models has been the great deal of time spent learning languages in which models are written and keeping track of the specific variable names and equations within models. To remove the excessive psychological burden from busy executives and to refocus attention towards the actual behavior being replicated, Inter/Consult has been researching development of highly supportive user interfaces to models. These interfaces prompt users by stating the nature of the model’s assumptions then asking what changes they would like to make. Through this on-line question-and-answer dialog users can build and compare scenarios without prior knowledge of computer languages and mathematical formulas or specific model components. Our paper presents reactions to the interface by members of the graphic arts industry who have used it. We discuss further improvements which are being made to the interface to make our models more accessible to non-expert users. Finally we explain why we feel that tightly-focused, easy-to-use, dynamic simulation models are of invaluable benefit to any industry such as graphic arts where craft-oriented skills are being replaced by rapidly evolving new technologies.
A disaggregate population model of China is presented. The age structure is represented by one-year cohorts. Urban and rural populations are distinguished. Birth and death rates, family size, life expectancy, and other demographic variables are determined endogenously. The model can be used to analyze population problems and to project population size, the age structure, the adult labor force, the elderly population, and so on. The model can be used in two modes. It can be used to project the consequences of various exogenous fertility levels. Alternatively, birth rates and fertility can be determined endogenously by economic inputs such as food supply, GDP, and services. The model incorporates socioeconomic factors important in the demographic transition, such as the effect of perceived life expectancy on fertility, the effects of traditional values, and the ability of government to influence family fertility choices. The model can be used to evaluate policies and programs designed to control population growth, such as delayed marriage age, improved contraception, and restrictions on family size. The model requires industrial, service, and food output per worker as inputs, and also the level of pollution. The model should be thought of as a component of a comprehensive planning model which generates these inputs endogenously. Based on the system dynamics approach to modeling complex systems, the model is implemented in the DYNAMO simulation language.
In this paper some of the ideas of Ortega y Gasset about the dynamics of history have been gathered and organized according to the system dynamics diagrams. A cyclic process, characteristic of every normal course of history, is described as well as the dynamics hypothesis responsible for it. Human life, as far as it affects history, is shown as being composed of five age groups each of them covering fifteen years of life. Two of these groups, two generations acting simultaneously in the field of history, are presented as taking the main responsibility for the dynamics of history.
“Generic models,” as the term is emerging, denotes a model representing the underlying causes of commonly occuring sets of problems, whose purpose is for education, rather than for policy analysis per se. Preliminary uses of generic models have been an exciting and efficient means of transmitting insights. This paper is a status report on the modeling of a company's conversion to a new production or product technology. Based on information sources including in-depth interviews within such companies, the authors' previous experiences, and published surveys and cases, the planned model focuses on management goals, staffing, and acquisitions of the skills necessary to deal with the new technology or product. Although the model does not explain every (complete or partial) implementation failure, it seems relevant to a significant fraction of such failures. The authors intend to develop the model and curriculum materials for management education and portions of university courses on technology management.
This paper presents a computerized system dynamics game in which the player makes "annual" decisions controlling the availability and evaluation of a new medical product with uncertain potential and possible (though initially undetected) side effects. The game has been implemented using the popular spreadsheet program Lotus 1-2-3. This program has on-screen display capabilities allowing for the construction of a user-friendly game that requires no knowledge of system dynamics. A detailed discussion of game mechanics is followed by a description of a classroom experience which led to further development of the original version of the game and some general insights about game-building.
Within the MIT System Dynamics National Model, the risk-free interest rate is determined jointly by the normal interest rate and by liquidity. The normal rate is the rate which agents believe would obtain under normal circumstances, in the absence of transitory pressures. The normal rate continually adjusts to new interest rate conditions. During times of deficient liquidity, agents will increase the risk-free rate above the normal rate. The converse also holds. The risk-free rate will continue to adjust until pressures in the system are relaxed. Estimation results support the national model theory of interest rate formation.
Although there are more than 3000 end uses of aluminium in the world and more than 300 in India, yet there are five sectors viz. power, consumer durables, transport, building consturction canning and packaging which account for more than 90% of aluminium consumption. To study the dynamics of demand of aluminium in these sectors, system dynamics model having various sectors viz. Population, economy, power, consumer durables, construction, packaging and canning, transport and aluminium consumption model has been simulated from 1970 to 2000 A.D. using dynamo.
A method is described and illustrated for explicit incorporation of and computation with ranges of initial conditions, functions, and parameter values in dynamic models using interval analysis. This approach is neither a statistical nor fuzzy set analysis but instead utilizes interval arithmetic which is particularly well suited for computerization. When a dynamic model is couched in interval analytic terms, ranges of all possible solutions are generated allowing not only an analysis of ranges of behavior modes but for sensitivity and stability analysis to be performed as a natural part of the model. Moreover, uncertainties such as specification, numerical method (e.g., numerical integration), and roundoff errors can also be analyzed in conjunction with or separate from the interval dynamic model.
Mid-volume, mid-variety operations characterize flexible manufacturing systems (FMS) or job-shops found in most factories. Profitability of FMS depends upon effective scheduling of material flow, machine use, staffing, and buffer capacities. Many systems adjust to changes in demand and equipment failure in the long term. In the short term, however, large changes may occur in inventories, staffing requirements, and machine utilization. In general, these large changes reduce production efficiency and profits. An approach is demonstrated for attenuating or eliminating changes or swings in a system when there occurs some abrupt change. Delays and delay parameters in the system model are adjusted, subject to practical constraints, to produce a smooth and rapid transition after the change. A simple econometric model is used for illustration. A symbolic and algebraic manipulation language is required to implement the approach.
Burnout is a problem associated with work in social service organizations. It is characterized by loss of energy, negative attitudes, and decreased performance. This system dynamics model encompasses the literature on burnout and belongs to a general class of stress and motivational models which describe problems of alcoholism and sexual harassment in the work place, etc. The gap between performance and professional expectations generates physical and psychological fatigue, which decreases involvement and performance. Supervisors frequently ignore the workers' problems, but will initiate structure when quality is perceived to decrease. The gap between expectations and performance may account for burnout initially, but cannot account for maintaining burnout after expectations decrease. Learned helpless may be the mechanisms that sustains burnout.
Many electric utilities have a heavily debt-laden capital structure. A number of factors have contributed to this situation, but chief among them is the theory that increased debt improves a corporation's earnings per share. This theory is derived from a relatively simple financial model which relates earnings per share, capital structure, interest costs, and income. Using a more comprehensive model, this paper shows that reducing debt as a percentage of capital structure can improve the interest coverage, earnings per share, and market price per share of electric utilities.
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.
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.
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.