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![FLO
WS
• Faucet and drain
• Rates of change
• Verbs
• How a system is changing
• Exist over [a period of] time
• Disappear when all activity freezes
Fill or drain stocks
(only way to change a stock)
Create dynamics in system](https://image.slidesharecdn.com/csdpractical3-240219214837-c58de22a/85/complex-system-and-dynamics-basic-dynamic-systems-models-7-320.jpg)
![environmental modelling_lecture_khwopa [Autosaved].pptx](https://cdn.slidesharecdn.com/ss_thumbnails/environmentalmodellinglecturekhwopaautosaved-250518082519-8c595a41-thumbnail.jpg?width=640&height=640&fit=bounds)
complex system and dynamics basic dynamic systems models
- 1. DYNAMIC MODELING Stocks and Flows Dr.KhurramIqbal Ahmad Khan Assistant Professor, CEM, NUST
- 2. CLASS OUTLINE Stocks and Flows– operational language • Stock definition and examples • Flow definition and examples • Stocks and flows together
- 3. STOCK S • Bathtub (orany other container) • Accumulations • Nouns, i.e., things and states of being • Current state of system • Exist at a point in time • The only things that still have a value when all activity freezes
- 4. PHYSICAL (AKA TANGIBLE) STOCKS StaffBank Balance Inventory Carbon Land Tasks Pollution Population Zebras Cars Houses Jobs Note names have first-letter capitalization
- 5. INTANGIBLE STOCKS Anger Knowledge Frustration Satisfaction Happiness Reputation Quality HungerSelf Esteem Commitment Trust Love
- 6. NOT A STOCK • Verbs:run, drive, jump, fall, swim • Adjectives: red, fast, sporty, pretty, scary • Adverbs: slowly, recently, very, carefully, today
- 7. FLO WS • Faucet anddrain • Rates of change • Verbs • How a system is changing • Exist over [a period of] time • Disappear when all activity freezes Fill or drain stocks (only way to change a stock) Create dynamics in system
- 8. buying building creating hiringsaving producing PHYSICAL FLOWS Note names are all lowercase burning fossil fuel filling wetlands assigning polluting being born capturing
- 9. INTANGIBLE FLOWS building up dissipatinggrowing losing learning increasing improving eating earning
- 10. NOT A FLOW • Nouns:car, house, tree • Adjectives: red, fast, sporty, pretty, scary • Adverbs: slowly, recently, very, carefully, today
- 11. STOCK OR FLOW? • profit •cumulative profit • yesterday • zebras born • births • Other flows: unit sales, revenue, expense, deaths
- 12. COMBINING STOCKS AND FLOWS(SENTENCES) • inflows hiring Staff saving Bank Balance burning fossil fuel Carbon learning Knowledge completing • outflows Tasks dying Population dissipating Anger eating Hunger
- 13. eating Hunger UNIT S • outflows hiring Staff saving Bank Balance Carbon learning Knowledge completing Tasks dying dissipating Anger tasks tasks/time $ $/time GT GT/time k-units burning fossilfuel k-units/time worker s • inflows workers/time people Population people/time a-units a-units/time kcals kcals/time
- 14.
- 15. RULE 1: RESPECT UNITS Salary Levels Employee Motivation contributing $m-units ???/time Staff placing ads workers ads/month using birth control people Population uses/person/month Salaries must go down to improve motivation
- 16. RULE 2: RESPECT CONSERVATION assumesdeaths absorbed by envir. learning does not take away someone else’s knowledge saving dying • Material can neither be created nor destroyed • Except at clouds: infinite sources and sinks at the model boundary Bank Balance Population learning assumes not limited by money supply • Except intangibles Knowledge
- 17. NEVER CONSERVE NON- PHYSICALQUANTITIES Customer Dissatisfaction Employee Dissatisfaction leading to d-units d-units d-units/week Units check But does customer lose dissatisfaction as employee’s increases?
- 18. INFLOW BEHAVIOR • Constant zero •Constant (non-zero)
- 19. INFLOW BEHAVIOR • Linearly increasing •Linearly decreasing
- 20. INFLOW BEHAVIOR • Step upthen down
- 21. EXAMPLE In this smoggycity, the air pollution continues to increase without limit, making it hard for the health-conscious citizens to do anything without coughing.
- 22. OUTFLOW BEHAVIOUR • Constant zero •Constant (non-zero)
- 23. OUTFLOW BEHAVIOUR • Linearly increasing •Linearly decreasing
- 24. EXAMPLE There is alimit to the fossil fuels available to us on this earth. With more and more people and greater demand for energy per person, we will run out very soon.
- 25. INFLOW AND OUTFLOW BEHAVIOUR • inflow= outflow (steady-state or equilibrium) • inflow > outflow (constant) • inflow < outflow (constant)
- 26. EXAMPLE A firm’s customerbase is growing quite well, gaining a constant number of customers each year. Despite this, at a certain point, the size of the customer base starts to fall. How can this be?
- 27. A CLOSER LOOK Page 1 0.003.75 11.25 15.00 7.50 Months 1: 2: 3: 1: 2: 3: 1: 2: 3: 10 0 25 4 1: Customers 40 8 2: gaining 3: losing 1 1 1 1 2 2 2 2 3 3 3 3
- 28. SUMMA RY • Stocks andflows provide an operational view • Stocks are nouns, accumulations • Flows are verbs, rates of change • Combine them to make sentences • Be careful of units and conservation
- 29.