1. Introduction to Computing
for Complex Systems
(Lab Session 3)
daniel martin katz
illinois institute of technology
chicago kent college of law
@computationaldanielmartinkatz.com computationallegalstudies.com

2. A Few Books
Worth Considering

3. Goals for Today
Finish Exploration of the
Forest Fire Model
Begin exploration of the
Schelling Segregation Model

4. Every item in our Model is:
Important Principles from
Our Last Session
(1) Defined within the Model
(2) Is a Primitive that is defined
in the Netlogo Dictionary
OR
(remember we can think of primitives
as the raw materials of models)
(such as in Globals, Breeds
or in a subroutine)

5. Exploring the
Forest Fire Model
http://ccl.northwestern.edu/netlogo/models/Fire
(CONDT.)

6. The Forest Fire Model

7. The Forest Fire Model

8. 3-D Forest Fire Model

9. (1) Modify the Color of the
Forest to Blue
(2) Make the Fire Move North to
South Instead of West to East
How Did We Do?

10. Modify the Color of the
Forest to Blue

11. What Elements of the Code
Do We Modify?

12. The Forest Fire
Model
Procedures

13. The Forest Fire
Model
Procedures

14. Make the Fire Move North to
South Instead of West to East

15. Make the Fire Move North to
South Instead of West to East

16. What Elements of the Code
Do We Modify?

17. The Forest Fire
Model
Procedures

18. The Forest Fire
Model
Procedures
Try this
Instead:

20. In what sense is this model random?
In what sense is this model deterministic?
Thinking conceptually
about the model procedures
all of these models involve a mixture
of determinism and randomness

21. In what sense is this model random?
Thinking conceptually
about the model procedures
Placement of the patches
subject to the selected density level

22. Watch the Model in 3D

23. Watch the Model in 3D

24. Watch the Model in 3D

25. Watch the Model in 3D

26. In what sense is this model deterministic?
Thinking conceptually
about the model procedures
The fire is really for G.U.I. purposes
result is basically already
determined before the fire spreads

27. Back to the
Forest Fire
Model
Procedures

28. relies upon:
if not any? stop
ask fires
ask neighbors4
fade-embers
ignite
tick
The ‘To Go’ Procedure

29. if is a condition and you can think of it as:
if x condition is met than do action y
(otherwise move on to the next line)
The ‘To Go’ Procedure

30. This is going to
kill the model if
condition is
achieved
vs.
Forever
Button
Once-only
Button
The ‘To Go’ Procedure

31. Why is this Arguably the KEY piece of code?
What does it mean in plain english?
The ‘To Go’ Procedure

32. What is neighbors4?
Remember our basic rule:
The ‘To Go’ Procedure
It is defined within the program
or it is one of the netlogo primitives

33. The ‘To Go’ Procedure

34. Neighbors and
Neighbors4
turtle turtle
neighbors4 neighbors
(think of
this as the
8 neighbors)
turtle

35. (a) we are asking “fires”
The ‘To Go’ Procedure
(b) to ask their 4 neighbors
(c) the 4 neighbors that are green
(d) to run the “ignite” protocol
(e) and then set their breed to embers
(f) now run the “fade-embers” protocol

36. The ‘To Go’ Procedure

37. The ‘To Go’ Procedure

38. The ‘To Go’ Procedure
When is this finally going to halt?
It is a forever button which can be
halted using “STOP”
“STOP” is triggered when the
“if” condition is satisfied

39. Lets Discuss Some
Extensions of The
Forest Fire Model

40. Extensions of The
Forest Fire Model
What are the actual dynamics that
generate and sustain forest fires?
What else could we incorporate
into this model?

41. A Non-Exhaustive List
Differential Levels of Moisture
Variable Terrain (Rivers, etc.)
Prior Interventions (Firewalls, etc)
Wind and other Weather Patterns

42. Some of the
Existing Extensions

44. different forms of implementation
may impact the results
Implementation Matters
different forms of implementation may
be more qualitatively appropriate
sophistication regarding implementation
allows you to be a more critical
consumer of scholarship

45. the neighbors4 example

46. Neighbors and
Neighbors4
turtle turtle
neighbors4 neighbors
(think of
this as the
8 neighbors)
turtle

47. Neighbors and
Neighbors4
neighbors
(think of
this as the
8 neighbors)
what did the
implementer of
the model decide?
neighbors4
decided that the
fire could not move
diagonally
this is probably
not qualitatively
reasonable

48. Step 1: map the dependancies
Step 2: learn the syntax and
functionality for all
unknown primitives
Protocol to Decode
3rd Party Implementation
Step 3: read each line of code and
determine what it doing

50. Mapping
of the
Code

51. just some examples of primitives from the
dictionary that we have already learned
Protocol to Decode
3rd Party Implementation

52. Next We Went Line by Line
Through the Code

53. Step 4: sketch a procedures map
that follows the chronology
of your program
There is one additional step that
often proves useful
Protocol to Decode
3rd Party Implementation
Particularly when you are writing a
model from scratch

54. Very Rough
Sketch of the Fire
Procedures Map
(1)
(2)
(1)(a)(i)
(1)(a)
(1)(a)(ii)
(1)(b)
the point is just to aid in
your understanding
(2)(a)
(2)(a)(i)
(2)(a)(i)(I)
(2)(b)
(2)(b)(i)
(3) - End
Loop Until “if”
Condition is met

55. The Value for Global Must Get “Set”
Somewhere in the Model Procedures
Globals -- one other note

57. Mapping
of the
Code

59. Introduction to the
Schelling
Segregation Model

60. What Does this Title Mean?
What is the micro to
macro disconnect?
relationship to the
ecological inference
fallacy?

61. Schelling Social Segregation Model

62. Schelling Social Segregation Model

63. Schelling Social Segregation Model

64. Schelling Social Segregation Model

65. Schelling Social Segregation Model

66. Schelling Social Segregation Model

67. Schelling Social Segregation Model
versus
note: stopped model before % unhappy = 0

68. Schelling Social Segregation Model
Test these
Parameters
and report
Results

69. Schelling Social Segregation Model

70. Schelling Social Segregation Model

71. Schelling Social Segregation Model

72. Schelling Social Segregation Model
versus

74. Schelling Social Segregation Model

75. the full
model

77. Print This and Draw the
Connections for a Full Map
of the Schelling Code

78. Mapping of the
Schelling Code
(%-similar-wanted is a slider)

79. Learn the Syntax and
Functionality for all
unknown Primitives
(starting with “to setup”)

80. Again this is the conditional “if” statement
It is relying upon “number”
Is number a netlogo primitive?

81. It is the name of the slider
How could I rename this “totalagents”?
Take 5 minutes and Try to Figure it out

82. (1) Right Click (ctrl + Click on Mac)
on the “number” slider
(2) change the
global variable
name from “number”
to “totalagents”
Modifying the name
(or values) of a Slider

83. Modifying the name
(or values) of a Slider
Notice the
error Message
Must Change all
instances from
“number” to
“totalagents”
Then double
check by hitting
the “check”
Button

84. We have learned a small exception to our rule
Revised Rule --> everything in the model:
(1) defined somewhere in the code
(2) is a primitive
(3) it is something like a slider

85. What is this doing in plain english?
clear everything
if the end user selects a slider value that
exceeds the number of patches
tell that end user to modify and try again

87. (1) Close Netlogo
(2) Discard the Changes
(3) Restart the Segregation model
Quick Reset

88. Open the Schelling
Segregation Model
Delete all
procedures except
those shown to left
What is has this
done to the model?
<Only Red Turtles>
<“Go” button is red>

89. What is this doing in plain english?
asks all of the patches
to randomly “sprout” 1 turtle per patch
and make that turtle color = red

90. What is this doing in plain english?
now take half of those turtles
and set turtle color = green

91. We Need to see
What “update-
varables” is
Actually Doing

92. Here we are going to “set” some of our
“turtles-own” variables

93. “Set” the Turtles-own Variable “similar-nearby”
to the count of “turtles-on” neighbors (8 of them)
but only those with color = my color

94. “Set” the Turtles-own Variable “similar-nearby”
to the count of “turtles-on” neighbors (8 of them)
but only those with color = not my color

95. Take a look at what is happening here
The “happy?” condition is going to be important
involves an agent by agent comparison of the
spread between “similarity-wanted” & “similar-
nearby”