Thomas J. Manetsch

Time-Varying Distributed Delays and Their Use in Aggregative Models of Large Systems

The distributed delay has found widespread application in the modeling of aggregative processes involving the flow of entities with random transit times through a given process. In most of these applications it is assumed that the mean entity transit time is fixed. There are, however, a number of important applications in aggregative economic, physical, social, and biological systems in which the mean entity transit time is time varying. A time-varying distributed delay model is developed along with a Fortran subroutine for its simulation as part of a larger system model. Examples illustrate applications of this time-varying distributed delay model to aggregative biological and economic processes.

Toward efficient global optimization in large dynamic systems-the adaptive complex method

The efficient solution of global optimization problems in large dynamic systems requires methods that are robust, do not require analytical expressions for the objective function or its derivatives and require function evaluations only on the order O(n), where n is the dimension of the search-variable space. The adaptive complex method operated in a staged feed-ahead mode has been found to possess these qualities. The method is described along with tests using classical multimodal functions. The tests indicate that the method is efficient relative to other methods. Tests with higher-dimension multimodal problems (with spaces of dimension 22 and 36) are described, and the results indicate that the method can be employed to solve efficiently much larger problems of the class described. >

Simulation of Nigerian Development: Northern Region Model

A multidisciplinary team is currently studying the applicability of computer simulation to problems of agricultural sector development in Nigeria. The program has as one of its major objectives the exploration of simulation as a tool for aiding policy makers of that country concerned with meeting the nutritional needs of the population, generation of foreign exchange earnings and raw material inputs for industrialization, and other important questions relating to long-run development of the agricultural sector and its interaction with nonagricultural development. While the project is localized in a particular country, models are being developed with adaptability to other developing areas of the world as a major objective. To date, a model of the northern region of the country has been developed which will be linked to a southern model currently under construction. The structure of the northern model is described in some detail as an example of the application of simulation to a macroeconomic system. Preliminary tests of this model are discussed and an assessment of the capabilities and limitations of this approach to planning development in emerging countries is given.

Simulation approach to development planning with nigerian and korean applications

The problems of planning for economic development arise from the interplay of the political, social and economic subsystems of a developing country. These problems are characterized by the uncertainty necessarily inherent in any process of planning for the future-uncertainty arising both from the quantity and quality of available data and from the difficulties of fore-casting how a large-scale system of complex interactive and feedback relationships will respond to policy inputs. In this paper, we discuss generalized system simulation as an approach to dealing with these problems. We view this approach as a flexible, iterative, problem-investigating process that includes problem formulation, mathematical modeling, testing and refinement of the model, and model application to problem solution-all in close consultation with decision makers. This discussion will be followed by a brief description of policy-oriented, system simulation models of the Nigerian and Korean economies. The models consist of detailed regional agricultural submodels, an aggregated national nonagricultural submodel and components which model population and, in the case of Nigeria, the interregional trade in food. The policy options the current models are capable of investigating include programs to modernize agricultural production and various forms of tax and commodity marketing board pricing policies. Finally, we outline how the generalized system simulation approach could be implemented within the development-planning and policy-making process and indicate some of the capabilities and limitations of the approach.

Use of concurrent processing with the adaptive complex method for global optimization of large dynamic systems

A modified version of the adaptive complex method for global optimization is described that parallelizes a procedure that is computationally serial in nature. The modified method assigns n/sub p/ processors for parallel execution. Simulation tests and an implementation with parallel hardware indicate that speed-up factors with the modified method are nearly linear with n/sub p/ up to about 0.1k where k is the number of vertices in the optimizing complex. Since k increases linearly with problem size, the modified method can significantly reduce computation times for large optimization problems. >

Computer Simulation as a Planning Tool in Developing Economies

OMPUTER simulation is a systems analysis tool which utilizes subSject matter theory, certain mathematical structures, programming logic, and empirical analyses to condense a complex system into a mathematical formulation duplicating the essence of the real system. Thus, it focuses on the whole system of interrelationships within the selected universe of inquiry. Recently, computer simulation has begun to be explored as an economic development-planning and decision-making tool which can simultaneously incorporate multiple objective or criterion functions and uncertainty in analyzing the results of various policy combinations over the course of time. An interdisciplinary research team (primarily agricultural economists and systems scientists at Michigan State University) is currently simulating major elements of the Nigerian agricultural economy. Our current efforts [4] and review of some of the previous literature [1, 2, 3] prompt us to evaluate simulation tentatively as a planning and policy-making tool at the macro level, especially in developing economies. The following discussion will focus on the capabilities of an economy simulation model and the resources required to develop it.

The United States Plywood Industry - Systems Study

The U. S. plywood industry is analyzed as a feedback system and simulated on a large-scale digital computer. An industry of thousands of interacting firms is approximately represented by a model of seven interacting sectors by grouping together firms which tend to behave homogeneously in response to the same input variables. The seven sectors include two producing sectors representing, in the aggregate, independent mills of the industry and mills integrated in their organization with wholesale warehouses. Three wholesale sectors represent aggregations of independent jobbers, jobbers integrated organizationally with producers, and office wholesalers who hold no physical inventory. Two retail sectors represent, in the aggregate, retailers and users who buy in box-car-load lots and those who buy in less than box-car-load lots. Description of the independent mill and independent jobber sectors are presented in some detail because of the key role these firms play in the determination of market price. The market price mechanism is discussed along with the method employed to represent, in the aggregate, the information and material handling lags in the system. Preliminary tests of the simulation model are compared with industry data.

A model for studying national‐level nutrition planning issues in poor countries

A computer simulation model is presented for studying national level issues as they affect the well being of the poor in developing countries. The model permits the user to explore the impact of various national‐level policies (such as government allocations to food production expansion, food aid to the poor, export expansion and public health and actions to change tax rates and to regulate food prices) upon a range of performance measures. The models performance measures, computed over a time horizon of interest, include: GNP, GNP growth rate, unemployment level, nutritional status and mortality rate (by population groups), government and private indebtedness, foreign indebtedness and inflation rate. Tests of model credibility are described as are tests to explore a number of issues related to nutrition planning in the national context.

Toward a comprehensive approach to nutrition/health planning for poor countries†

The paper addresses the problem of design for poor countries health/nutrition programs which are compatible both with national development goals and the constraints imposed by the village milieu in which human needs must be met. National level nutrition, health, family planning, food production and other programs are considered along with their sometimes conflicting impacts on variables such as nutritional status, infant/child mortality, personal productivity, population growth rate, employment, food production, GNP growth rate, government budget balance, foreign exchange balance and distribution of wealth. The paper describes an illustrative village level nutrition/health program designed to meet key human needs within realistic budget constraints and concludes with a discussion of useful roles computer models can play in comprehensive nutrition/health planning.

Bilateral Distributed Delays and Their Use in Modeling Classes of Distributed Parameter Processes

A bilateral distributed delay model is developed which is useful in modeling a number of reversible processes with or without losses. It is shown that as k, the number of stages in the delay process, becomes large the solution of the distributed delay model approaches that of a first-order partial differential equation with a number of important applications in modeling distributed parameter flow processes in the real world. It is also shown that with smaller k values the distributed delay model introduces z-axis diffusion which can be useful in modeling some flow-plus-diffusion processes. This paper is concluded with an illustrative application of the bilateral distributed delay.