Chap3: Vensim model Mini publishing company

Question 1

Model Mini-Publishing Company The model represents the core of a very small publishing company which produces only one book. We are interested in how the amount of copies of this book in stock responds to the arrival of new books from the production department, and to outgoing books due to sales. Is the Model a static or dynamic model?

Answer 1

This Model is an example of a simple static (linear) system, it is static (as opposed to dynamic), because it contains no feedback loops. However, playing with this model opens many important insights into how stocks and flows work

Question 2

What are the main variables of this model (with units) ?

Answer 2

• Books in Stock (variable type: stock, unit: books, initial value: 10000 books) • Production (variable type: flow, unit: books/week) • Sales (variable type: flow, unit: books/week)

Question 3

What are the time related definition? give example of initial values.

Answer 3

Time related definitions (Menu Model/Settings) • Time Unit: week • Simulation Time Span: 50 weeks (Initial Time = 0, Final Time = 50) • Time Step = 1 (Vensim internal: one calculation step during one time unit. Often, smaller time steps e.g. 0.25, 0.125 are needed for sufficient accuracy, but no problem here)

Question 4

What happens in the next scenarios? Scenario 1: Sales equal Production Set Production = 1000 books/week and Sales = 1000 books/week Scenario 2: Really bad Sales Production = 1000 books/week, Sales = 0 books/week Scenario 3: Production drop out Production = 0 books/week, Sales = 100 books/week

Answer 4

Scenario 1: Sales equal Production –>No change in stock size alwaya 10 000 books

Scenario 2: Really bad Sales –> Stock increases

Scenario 3: Production drop out –> Stock decreases

Question 5

Stock and flow diagram components are ?

Answer 5

• sources and sinks - stocks - arrow of flow of materials - logic arrows - Valve symbol ( Fluid mechanics)

Question 6

What happens in the next scenarios? Scenario 4: Not so bad Sales Production = 1000 books/week, Sales = 100 books/week Scenario 5: Book Hype in Week 20 Production = 1000 books/week The sales are constant at 1000 books/week up to week 19. In week 20 the sales are 5000 books/week, after that, they drop back to constantly 1000 books/week again. This can be modeled in Vensim as follows: Sales = 1000 + 4000 * PULSE(20, 1)

Answer 6

Question 7

Scenario 6: Restoring the Inventory after Hype I After the book hype, we want to bring the inventory (books in stock) back to its original value of 10000 books. e.g. Production = 1000 + 4000 * PULSE(30, 1) Sales = 1000 + 4000 * PULSE(20, 1)

Scenario 7: Restoring the Inventory after Hype II How to restore the inventory if production can maximally deliver 1500 books/week? Production = 1000 + 500 * PULSE(30, 8) Sales = 1000 + 4000 * PULSE(20, 1) Scenario 8: Hype doesn’t come What if the managers expected a book hype (and scheduled production as above), but the hype doesn’t occur? Production = 1000 + 500 * PULSE(30, 8) Sales = 1000

Answer 7

Question 8

Last scenario hype doesn’t come: Managers except a hype and schedule production change, but sales hype doesn’t come :(

Answer 8