Poster Vensim Repast
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This document describes a software framework that integrates agent-based simulations with system dynamics models. It allows agents in an agent-based simulation to call system dynamics models. The framework uses Java for the agent-based components and interfaces with the system dynamics software Vensim using a DLL. An example application to a supply chain model is provided, where manufacturer agents run a system dynamics inventory control model in each time step. The integration allows leveraging the strengths of both approaches for more flexible modeling of dynamic systems.
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Poster Vensim Repast
- 1. A Software Interface Between System Dynamics and Agent- Based Simulations
- 2. A study by Andreas Gr旦ler, Myrjam Stotz, and Nadine Schieritz Mannheim University, Germany
- 3. Agent-Based Simulation Whereas in system dynamics the internal structure of a system determines its dynamic tendencies, in the agent- based simulation the dynamic behavior of a system arises from the behavior of its elements, the agents, and the interactions between them: System Dynamics Agent-Based Simulation Basic building block Feedback loop Agent Unit of analysis Structure Agents' rules Level of modeling Macro Micro Perspective Top-down Bottom-up
- 4. Scientific Problem Agent-based simulation and system dynamics use computer simulation to investigate social and economic systems characterized by non-linearity, delays and feedback processes. Both concentrate on understanding and qualitative prediction of systems behavior. An integration of both approaches might be fruitful.
- 5. The Software Used A software framework for creating agent based simulations using the Java language A visual modeling tool for system dynamic models The Vensim DLL allows you to call Vensim functions from other applications
- 6. The Technical Integration At least two Java classes have to be programmed: the simulation environment and the agents class Java class of the simulation environment Based on a class given by RePast Builds and manages the agents Manages the simulation Provides a graphical user interface Java class of the agents Represents the mental model of the agents Builds a Vensim object to communicate with Vensim via the Vensim DLL Vensim object (provided by Vensim) Calls the Vensim DLL Manages the transfer of data and commands between the agent- class and Vensim provides creates creates calls
- 7. An example from Supply Chain Management Supplier Agent Manufacturer Agent1 Manufacturer Agent2 Manufacturer Agent3 Behavior of the manufacturer RePast VensimDLL Agent-based simulation System Dynamics Behavior of the manufacturer Behavior of the manufacturer
- 8. The Agents Behavior Inventory Acquisition Rate Shipment Rate Desired Acquisition Rate Acquisition Adjustment from Inventory Desired Inventory Expected Order Rate Change in Exp Orders Inventory Adjustment Time Desired Inventory Coverage Time to Average Order Rate Order Fulfillment Ratio Table for Order Fulfillment Supply LineOrders Placed Rate Acquisition Lag Adjustment for Supply Line Desired Supply Line Orders Placed Supply Line Adjustment Time Customer Order Rate B Order Fulfillment B Inventory Control B Supply Line Control - - + + + + + - - + + - + + + - Desired Shipment Rate + Maximum Shipment Rate Minimum Order Processing Time + + - - + Inventory Coverage + - Safety Stock Coverage + + + Customer Orders Backlog Backlog Change Rate + - + Supplies Received Init Supply Line Init Inventory Init Expected Order Rate Init Customer Orders Backlog + + In each step of a simulation the agent-based modeled manufacturers call this System Dynamics model (modified after Sterman 2000)...
- 9. The Simulation in RePast Start and stop a simulation Graphs represent the results of simulations In a probe map parameters of the simulation can be set
- 10. Conclusions The presented software solution provides a prototypical common technical platform to examine problems that suggest the integration of the two simulation concepts More flexibility is provided in modeling and simulating dynamic systems (using in each part of the model the method fitting best) The advantages of both methods can be used, their disadvantages can be reduced Skills in Java are necessary
- 11. Further Research Extend and improve the model technically, e.g. make simulations more user-friendly Use this platform to model other problems that suggest the integration of the two simulation concepts Use this software interface as a basis to model an integration with System Dynamics on macro-level and agent-based simulations on micro-level Investigate effects of combined methods on validity of models
- 12. References RePast: http://repast.sourceforge.net Venism: http://www.vensim.com Phelan, SE. 1999. A Note on the Correspondence between Complexity and Systems Theory. Systemic Practice and Action Research 12(3): 237246. Schieritz, N, Gr旦ler, A. 2003. Emergent Structures in Supply Chains: A Study Integrating Agent-Based and System Dynamics Modeling. Proceedings of the 36th Hawaiian International Conference on Systems Science, Wailea. Scholl, HJ. 2001a. Agent-based and System Dynamics Modeling: A Call for Cross Study and Joint Research. Proceedings of the 34th Hawaiian International Conference on Systems Science, Wailea. Sterman, JD. 2000. Business Dynamics Systems Thinking and Modeling for a Complex World, Boston.