IE 2030 Lecture 11 Introduction to System Dynamics

1. IE 2030 Lecture 11Introduction to System Dynamics

2. System Dynamics • Another descriptive model • Gives qualitative predictions and insights • Software tools exist (STELLA) • Main text: The Fifth Discipline by Senge • Senge’s book is on the non-technical, teaching side of the spectrum -one response to Dark Side

3. IE 2030 Lecture 11Today’s Core Concepts • Cause and Effect thinking, Influence or Causal Loop Diagrams • Feedback • Positive Feedback • Negative Feedback • Delay in Feedback Loops

4. Cause and Effect • Draw an arrow from cause to effect • ``Influence’’ or ``affect’’ may be a better term than “cause.” • Examples

5. Influence Diagrams • Place a “+” or a “-” at the arrow to indicate the kind of influence + means: the more of one, the more of the other (or less…less) - means: the more of one, the less of the other (or less…more)

6. Feedback Loops • Any directed cycle is afeedback loop • The arrows must take you back to where you started • Feedback makes systems complicated! • Examples

7. Principle: the most important causal influences are those that are within feedback loops

8. POSITIVE Even # of - signs Amplifying Reinforcing Growth, but also Decline Unstable NEGATIVE Odd # of - signs Balancing Stabilizing Often good! Stable equilibria Two Kinds of Feedback

9. Feedback Examples • A pencil falls • Standing on one foot

10. Delay • Taking a shower • Carrying a cup of coffee • Timing very important • Beer game, supply chains • Classic problem: when short-term influence is of one type, and long-term influence is of the other type

11. Administrative • Homework (old, new) • Project to turn in • New project: 1b, cashier validation • Data collection projects for sr. design • Spring break