1. Introduction to Computing
for Complex Systems
(Lab Session 2)
daniel martin katz
illinois institute of technology
chicago kent college of law
@computationaldanielmartinkatz.com computationallegalstudies.com

2. The Complete Code
for the
Forest Fire model

3. The Forest
Fire Model

4. the setup
procedure

5. 1st Operation is to Clear Everything

6. (a) The World Consists of
Turtles and Patches
(c) Default is Now “square”
(b) Turtle Can Assume
lots of Shapes
(d) What is the plain english
version of this line of
code?
(e) set-default-shape
for
turtles
to
“square”

7. (a) Call on Our Patches
Using “Ask Patches”
(b) But Only A Certain
Random Set of Patches

8. look at the brackets,
what do these brackets do?
we need to learn these primitives:
ask patches
random-float

9. The Ask Primitive

10. Random-Float

11. (a) Call on Our Patches
Using “Ask Patches”
(b) But Only A Certain
Random Set of Patches
(c) Patches With < “Density”
(d) Set Patch Color Green

12. With What Criteria?
pxcor = min-pxcor
[Notice The Brackets]
Again it is the
“ask” “patches with”

13. (a) Again it is the “Ask”
“Patches With”
(b) pxcor = min-pxcor
(c) To Ingnite
Here is where pxcor = min-pxcor
(i.e. Where Pxcor =0)

14. How Does It Know What
“Ignite” Means?
With What Criteria?
pxcor = min-pxcor
[Notice The Brackets]
To Do What?
Ignite
Consult Netlogo
Dictionary?
Is it there?

15. Here is How
(We Will Return
to This in a Few)

16. Lets Look at the Set Command

18. variable= initial-trees
value= count patches with
[patchcolor =green]
set variable value

19. variable= burned-trees
set variable value
value= numeric value of 0

20. notice how
within ‘setup’
these globals
are ultimately
assigned a
value

21. Modular Code:
notice how the
[ ignite ]
procedures are
defined below

22. “sprout-fires 1” ?

24. [ set color red]
note: color versus pcolor
this implies turtle not patch
(see dictionary for distinction)
fire turtle is set to red
“sprout-fires 1”
sprouting of a turtle
from breed = fires
and a 1 per patch
set pcolor black
setting patch color to black
set burned-trees to burned-trees +1

25. Modular Code:
now notice how
[fade-embers]
procedures are
defined below

26. [ set color color - 0.3]
makes the red darker
“ask embers”
embers are a breed
if color < red - 3.5
‘If’ is a conditional
(balance of the command is triggered
if condition is met)
Allows a slow fading of embers
What does color < red - 3.5 imply?

28. [ set color color - 0.3]
makes the red darker
“ask embers”
embers are a breed
[set pcolor color die]
if color < red - 3.5
‘If’ is a conditional
(balance of the command is triggered
if condition is met)
Allows a slow fading of embers
What does color < red - 3.5 imply?

29. We will focus
upon the ‘to go’
procedure in
the next class

30. 3-D perspective on the model
as it runs

31. notice how these turtles on the terrain

33. Exploration of the
Forest Fire Model
(1) Modify the Color of the
Forest to Blue
(2) Make the Fire Move North to
South Instead of West to East

34. Modify the Color of the
Forest to Blue

35. What Elements of the Code
Do We Modify?

36. The Forest Fire
Model
Procedures

37. The Forest Fire
Model
Procedures

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

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

40. What Elements of the Code
Do We Modify?

41. The Forest Fire
Model
Procedures

42. The Forest Fire
Model
Procedures
Try this
Instead:

43. What is a Dependancy?
In Class Exercise:
Identify Dependancies
in Fire Model
Why Does It Matter?
How Can We Represent Those
Dependancies in Our Code?

44. Lets Discuss
the Results

46. Mapping
of the
Code

47. 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

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

49. Watch the Model in 3D

50. Watch the Model in 3D

51. Watch the Model in 3D

52. Watch the Model in 3D

53. Watch the Model in 3D

54. 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