2. IE 2030 Lecture 11 Introduction to System Dynamics

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

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

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

6. 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)

7. Feedback Loops Any directed cycle is a feedback loop The arrows must take you back to where you started Feedback makes systems complicated! Examples

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

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

10. Feedback Examples A pencil falls Standing on one foot

11. 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

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