System Thinking Basics

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System Thinking Basics

• Pegah Nejat

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What is a System?

• It is composed of different parts.
• Much similar to a heap or a collection

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Dont be mistaken!

• A system is an entity which maintains its
• existence through mutual interaction
• of its parts.
• Too different from a heap or a collection!

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What is System Thinking?

• Looks at occurrences as a whole
• Looks at problems in their complete
• environment
• Studies the interaction of parts

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History

• Professor Jay Forrester recognized the need for a
  better way of testing new ideas about social
  systems.
• System dynamics was founded at MIT,1956.

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What kind of problems does it solve?

• Complex problems that involve helping many actors
  see the "big picture" and not just their part of
  it
• Recurring problems or those that have been made
  worse by past attempts to fix them
• Issues where an action affects (or is affected
  by) the environment surrounding the issue
• Problems whose solutions are not obvious

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Model

• A system exists and operates in time and space.
• A model is a simplified representation of a
  system at some particular point of time or space
  intended to promote understanding of the real
  system.

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A Trade-off

• How much detail in a model?
• If too little -gt risk of missing relevant
  interactions
• If too much -gt over complicated

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Simulation

• A simulation is the manipulation of a model in
  such a way that it operates on time or space to
  compress it.
• It enables us to perceive the interactions that
  would not otherwise be apparent because of their
  separation in time or space.

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Simulation cont.

• Simulations are usually iterative in their
• development i.e. you develop a model ,
• simulate it , learn from the simulation,
• revise the model and simulate again

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Simulation and modeling

• A discipline for developing a level of
  understanding of the interaction of parts and the
  system as a whole.
• Very much an art form!
• Become talented in it by building of models and
  simulating

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Software for modeling

• STELLA
• iThink (introduced in 1990)
• Both available through isee systems (formerly
  High Performance Systems Inc.)

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STELLA

• Introduced in 1985
• Friendly graphical interface
• Both simple and complicated models
• A learning environment
• Latest version 8

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STELLA?!

• By the way, STELLA stands for the
• following
• Structural Thinking Experimental
• Learning Laboratory with Animation

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Use STELLA to

• Map
• construct your model
• Model
• fill in the details
• Simulate
• feel free to ask what if ?!
• Communicate
• Every model tells a story!

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Useful links for further studying

• System Thinking resources
• System Thinking
• http//www.systems-thinking.org/
• MIT System Dynamics Group
• http//sysdyn.clexchange.org/
• High Performance Systems Inc.
• http//www.iseesystems.com/

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Steps to Modeling

• Grasp the system structure and dynamic relations
• Develop Casual Loop Diagrams (CLD)
• Translate diagrams into Stock Flow Diagrams (SFD)
• Simulate on computer!

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Step 1System Structure and Dynamics

• Population Example

Birth
Death
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Loops

• Reinforcing (R Loops)
• Balancing (B Loops)

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Influence cases in CLDs
Change in the same direction
Change in the opposite direction
Thing 2 increases
Thing 2 decreases
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Step 2Loop Diagram

Population
Birth
R
-
S
B
S
Death
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Equations

• P Population
• BR Birth Rate
• DR Death Rate
• dP/dt PBR PDR

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Step 1System Structure and dynamics

• Predator/prey example

Foxes eat
Rabbits are predated
rabbits
Foxes eat more
foxes
Foxes starve
Foxes dye of hunger
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Step 2CLD

O -
Rabbits

predation
O -
S
B
R
B
S
Foxes
Rabbit repro
-

O
Fox death
Fox repro
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Equations

• X prey population
• Y predator population
• a prey reproduction rate
• b predator reproduction rate
• c conversion of one prey into predators
• d predator mortality rate
• dX/dt aX bXY
• dY/dt bcXY dy

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Thanks for your attention!
Any Comments or Questions?