Simplicity, totality and change: a logistic viewpoint in inventory management
Abstract This paper demonstrates that even a simplified model works well when the model is revised from time to time. A new type of management problem results: easy-to-create models which cannot be validated.
The basic concepts of system dynamics optimization
This paper presents the fundamental concepts behind the use of heuristic optimization as a means of improving the behavior of systems as represented by system dynamics models. The philosophy of the approach is highlighted and the underlying software explained, as a prerequisite to developing some simple demonstration examples.
Synthetic design of policy decisions in system dynamics models: A modal control theoretical approach
Researchers and practitioners in system dynamics usually follow a trial-and-error process to design new policy decisions. They mainly use influence diagrams for this purpose. However, these diagrams portray the direction of influence but not its strength. Therefore, the process of policy design becomes time-consuming, especially for beginners and those working with insufficient computer facilities. This paper presents an alternative approach for policy design using modal control theory. Policy variables are treated as control variables by delinking them from other variables. This generally leads to greatly simplified models that are free from many nonlin-earities. Provided that this reduced system is linear and controllable, it is possible to synthetically generate control policies by modal control theory to ensure any prescribed degree of stability. These theoretical control policies then can be used to design realistic policy decisions. This approach has been used in a test example.