breeds [nodes edges]
edges-own [a b]
nodes-own [v]
globals [x-max y-max diam init-v-max reinit-v-max filename tick stoptick]

to setup
  ca
  set diam 4
  set init-v-max 3
  set reinit-v-max 10
  set x-max screen-edge-x - (diam / 2)
  set y-max screen-edge-y - (diam / 2)
  set filename "" ; change to collect images .. or use command center after setup
  set tick 0
  set stoptick 0  ; set to some number to stop, generally for image collections
  set-default-shape nodes "circle"
  set-default-shape edges "line"
  
  ask patches [set pcolor white]
  ask patches with [pxcor = 0 or pycor = 0][set pcolor gray]
  cct-nodes balls [
    set color yellow
    set size diam
    set v random-float init-v-max
    setxy random-float (x-max) * (2 * (random 2) - 1)
          random-float (y-max) * (2 * (random 2) - 1)
  ]
  if balls > 1 [ask nodes [
    connect-edge random-one-of nodes with [self != myself]
  ]]
end

to go
  if filename = 0 [setup]
  no-display
  set tick tick + 1
  ask nodes [
    set v v - gravity
    ifelse (abs (ycor + v)) <= y-max [
      set ycor ycor + v  ;set color yellow
    ] [
      set ycor y-max * sign ycor
      set v (- v)
      ifelse v >= 0 and v <= gravity
        [set v random-float reinit-v-max] ; set color red]
        [set v v - (sign v) * friction] ; set color blue]
    ] 
  ]
  ask edges [adjust-edge]
  display
  check-movie
  if stoptick = tick [stop]
end

to check-movie
  if length filename > 0 [
    export-graphics filename + substring "0000" (int log tick 10) 3 + tick + ".png"
  ]
end

to connect-edge [other-node] ; node proc: attach an edge between self and other
  hatch 1 [
    set breed edges
    set a myself
    set b other-node
    set color red
    adjust-edge
  ]
end

to adjust-edge ; edge proc: reattach to a & b nodes
  setxy xcor-of a ycor-of a
  set size distance-nowrap b
  set heading towards-nowrap b
  jump size / 2
end

;;;; Utilities
to-report sign [num]
  ifelse num < 0 [report -1][report 1]
end

@#$#@#$#@
GRAPHICS-WINDOW
204
10
565
392
19
19
9.0
1
10
1
1
1

CC-WINDOW
4
417
475
536
Command Center

BUTTON
7
69
62
102
NIL
setup
NIL
1
T
OBSERVER
T

BUTTON
68
70
123
103
NIL
go
T
1
T
OBSERVER
NIL

BUTTON
129
70
184
103
step
go
NIL
1
T
OBSERVER
T

SLIDER
6
34
184
67
balls
balls
1
20
5
1
1
NIL

SLIDER
7
193
183
226
gravity
gravity
0
5
1.0
0.25
1
NIL

SLIDER
8
235
184
268
friction
friction
0
1
0.25
0.25
1
NIL

TEXTBOX
11
10
183
31
Setup Parameters and Controls.

TEXTBOX
10
154
165
189
Runtime Parameters.\nCan change while running!

@#$#@#$#@
WHAT IS IT?
-----------
A very simple first graph (edges and nodes) model.


HOW IT WORKS
------------
Nodes are randomly created and linked, then are subject to gravity each step of the model.


HOW TO USE IT
-------------
Change the number of balls slider if you'd prefer a different value.  Click "setup" to initialize the nodes and edges.  Click "Go" to run the model, or click "Step" to manually run the model one step at a time.


THINGS TO NOTICE
----------------
Not much in the model, this is just a programming exercise to try the NetLogo edges and nodes facility.  You can read the code fairly easily to see how the graph is managed.


THINGS TO TRY
-------------
Move the two sliders "friction" and "gravity" while the model is running to see how they change the bouncing balls.  Change the code to play with the edges and nodes.


EXTENDING THE MODEL
-------------------
Have the nodes be attracted to the other nodes they are attracted to so that the nodes move in two directions.


NETLOGO FEATURES
----------------
Edges and Nodes!  The cool thing is the model NetLogo uses for edges: they are simply agents located at the center of the edge, and long enough to connect the nodes the edge connects.  Using floating coordinates lets the graph continuously morph.


RELATED MODELS
--------------
Check out the "layout" model which is a springs and forces model making the graph untangle itself.


CREDITS AND REFERENCES
----------------------
Seth Tisue sent me a very similar model to start out with .. Thanks!

@#$#@#$#@
default
true
0
Polygon -7566196 true true 150 5 40 250 150 205 260 250

circle
false
0
Circle -7566196 true true 35 35 230

line
true
0
Line -7566196 true 150 0 150 301

@#$#@#$#@
NetLogo 2.0.0
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@