models in ie lecture 13 system dynamics 2nd lecture systems archetypes
TRANSCRIPT
Models in IE Lecture 13
System Dynamics
2nd Lecture
Systems Archetypes
Lecture 13: Outline• More examples of causal-loop diagrams
• Glucose and Insulin– What is wrong?– How could such a bad system evolve?
• Natural systems, man-made systems– What to look for when systems behave poorly
• Common Patterns: System Archetypes– Success to the successful– Escalation
Analysis of an argument
or
How to make a mountain out of a molehill
A’sanger
B’sharshness
A’s harshness
B’sanger
+
+
+
+
Mountains out of Molehills
• Whose fault is it?– “You started it”
• Cause, effect, and blame are not clear in complex systems
Eat Candy
BloodGlucose
Level
HungerLevel
+
-
+
Eat Candy
BloodGlucose
Level
HungerLevel
+
-
+
InsulinProduction
Delay
-+
0
5
10
15
20
25
30
35
40
45
Candy MoreCandy
Candy
GlucoseInsulin
Oscillations that increase in amplitude over time are
a danger signal
Glucose and Insulin
• How could nature be so stupid?
• How could such an unfit system survive?
Nature isn’t stupid -- We are!
• 1st appearance of insulin regulation– 10,000,000-70,000,000
years ago
• 1st appearance of refined sugar– 1500 to 2400 years ago
Eat Complex
Carbohydrates
BloodGlucose
Level
HungerLevel
+
-
+
InsulinProduction
Delay
-+
Delay
Eat Complex
Carbohydrates
BloodGlucose
Level
HungerLevel
+
-
+
InsulinProduction
Delay
-+
Delay
Eat Candy
+
+
+
Natural & Man-Made Systems
合Natural systems have usually evolved so that timings work well
› Introduce a new element into a smoothly running system and you are lucky if timings remain good› As change rate of technology this
problem occurs more frequently
“The road to hell is paved with good intentions”
“The hurrieder I go,
the behinder I get”
“The harder we run, the more weseem to stay in the same place”
“When your best isn’t good enough…”
“I keep banging my head
against the same wall”
Understanding System Performance
GoodB en ch m ark
Im p roveU n d ers tan d w h y
F o cu s o ncom p on en t(tes t b e fo rein ves tm en t)
UnsatisfactoryF a ilu re ap p aren t
in on ecom p on en t
L in kag esTim in g s
F eed b ack
UnsatisfactoryN o ap p aren t
fa ilu re incom p on en ts
AssessPerform ance
System Archetypes
• Recurring, classic patterns
• Identified in Peter Senge’s book, The Fifth Discipline (Chapters 6-16, Appendix 2)
• Should become part of your permanent vocabulary
• Escalation• Balancing loop with
delay• Success to the
successful• Tragedy of the
commons• Limits to growth• Shifting the burden
For Next Class…
• Read about the different system archetypes
• Bring your book to class– open book QuizQuiz forecast w.p. .8
Feedback: class performance on homework
• Good but not excellent overall
• Don’t complain about 6 hours/week!– 2nd half of term much harder
• Many of the harder problems are difficult conceptually, not technically– try harder– try more than once (many already do).
• Most work on Little’s Law problem, (6a.m, 6pm) was unsatisfactory.
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