globals [
  time           ;; how many clock ticks have passed in the model
  color-mode     ;; 0 = normal, 1 = when heard, 2 = times heard
  clique         ;; how many patches have heard the rumor
]

patches-own [ 
  times-heard    ;; tracks times the rumor has been heard 
  first-heard    ;; clock tick when first heard the rumor 
  just-heard?    ;; tracks whether rumor was heard this round -- resets each round 
] 

;;; setup procedures

to setup [seed-one?]
  ca
  set time 0
  set color-mode 0
  set clique 0
  ask patches 
    [ set first-heard -1
      set times-heard 0
      set just-heard? false
      recolor ]
  ifelse seed-one?
    [ seed-one ]
    [ seed-random ]
  update
  do-plots
end

to seed-one
  ;; tell the center patch the rumor
  ask patch 0 0
    [ hear-rumor ]
end

to seed-random
  ;; seed with random number of rumor sources governed by init-clique slider 
  ask patches with [times-heard = 0]
    [ if (random-float 100.0) < init-clique
        [ hear-rumor ] ]
end

to go
  if not any? patches with [times-heard = 0]
    [ stop ]
  set time (time + 1) 
  ask patches
    [ if times-heard > 0
        [ spread-rumor ] ]
  update 
  do-plots
end

to spread-rumor  ;; patch procedure
  locals [neighbor]
  ifelse eight-mode?
    [ set neighbor random-one-of neighbors ]
    [ set neighbor random-one-of neighbors4 ]
  if wrap? or not wrapped-neighbor? neighbor
    [ set just-heard?-of neighbor true ]
end

;; the neighbors and neighbors4 primitives always wrap,
;; so if WRAP? is false we need to reject "neighbors" that
;; are only neighbors because of wrapping
to-report wrapped-neighbor? [neighbor]  ;; patch procedure
  report (abs (pxcor - pxcor-of neighbor) > 1) or
         (abs (pycor - pycor-of neighbor) > 1)
end

to hear-rumor  ;; patch procedure
  if first-heard = -1
    [ set first-heard time
      set just-heard? true ]
  set times-heard times-heard + 1
  recolor
end

to update 
  ask patches with [just-heard?]
    [ set just-heard? false
      hear-rumor ]
end

;;; coloring procedures

to recolor  ;; patch procedure
  ifelse color-mode = 0
    [ recolor-normal ]
    [ ifelse color-mode = 1
      [ recolor-by-when-heard ]
      [ recolor-by-times-heard ] ]
end

to recolor-normal  ;; patch procedure
  ifelse first-heard >= 0 
    [ set pcolor red ] 
    [ set pcolor blue ]
end

to recolor-by-when-heard  ;; patch procedure
  ifelse first-heard = -1
    [ set pcolor black ]
    [ set pcolor scale-color yellow first-heard screen-size-x 0 ]
end

to recolor-by-times-heard   ;; patch procedure
  set pcolor scale-color green times-heard 0 screen-size-x
end

;;; mouse handling

to spread-rumor-with-mouse
  if mouse-down?
    [ ask patch-at mouse-xcor mouse-ycor
        [ hear-rumor ] ]
end

;;; plotting procedures

to setup-plots
  set-current-plot "Successive Differences"
  set-plot-y-range 0 (count patches / 5)
end

to do-plots
  locals [new-clique]
  set new-clique count patches with [times-heard > 0]
  set-current-plot "Rumor Spread" 
  plot (new-clique / count patches) * 100
  set-current-plot "Successive Ratios"
  ifelse clique = 0 
    [ plot 1 ]
    [ plot new-clique / clique ]
  set-current-plot "Successive Differences" 
  plot new-clique - clique
  set clique new-clique
end


; *** NetLogo Model Copyright Notice ***
;
; This model was created as part of the project: CONNECTED MATHEMATICS:
; MAKING SENSE OF COMPLEX PHENOMENA THROUGH BUILDING OBJECT-BASED PARALLEL
; MODELS (OBPML).  The project gratefully acknowledges the support of the
; National Science Foundation (Applications of Advanced Technologies
; Program) -- grant numbers RED #9552950 and REC #9632612.
;
; Copyright 1998 by Uri Wilensky. All rights reserved.
;
; Permission to use, modify or redistribute this model is hereby granted,
; provided that both of the following requirements are followed:
; a) this copyright notice is included.
; b) this model will not be redistributed for profit without permission
;    from Uri Wilensky.
; Contact Uri Wilensky for appropriate licenses for redistribution for
; profit.
;
; This model was converted to NetLogo as part of the project:
; PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN
; CLASSROOMS.  The project gratefully acknowledges the support of the
; National Science Foundation (REPP program) -- grant number REC #9814682.
; Converted from StarLogoT to NetLogo, 2001.  Updated 2002.
;
; To refer to this model in academic publications, please use:
; Wilensky, U. (1998).  NetLogo Rumor Mill model.
; http://ccl.northwestern.edu/netlogo/models/RumorMill.
; Center for Connected Learning and Computer-Based Modeling,
; Northwestern University, Evanston, IL.
;
; In other publications, please use:
; Copyright 1998 by Uri Wilensky.  All rights reserved.  See
; http://ccl.northwestern.edu/netlogo/models/RumorMill
; for terms of use.
;
; *** End of NetLogo Model Copyright Notice ***
@#$#@#$#@
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1
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@#$#@#$#@
WHAT IS IT?
-----------
This program models the spread of a rumor.  The rumor spreads when a person who knows the rumor tells one of their neighbors.  In other words, spatial proximity is a determining factor as to how soon (and perhaps how often) a given individual will hear the rumor.

The neighbors can be defined as either the four adjacent people or the eight adjacent people.  At each time step, every person who knows the rumor randomly chooses a neighbor to tell the rumor to.  The simulation keeps track of who knows the rumor, how many people know the rumor, and how many "repeated tellings" of the rumor occur.


HOW TO USE IT
-------------
WRAP? is a switch which when set on allows the rumor to wrap top and bottom and left and right, as if the grid were on a torus. When set off, the rumor spreads as if the grid is bounded, without wrapping.

EIGHT-MODE? is a switch that determines whether at each time step the rumor spreads to one of four randomly chosen neighbors, or one of eight such neighbors.

As with any rumor, it has to start somewhere, with one or more individuals.  There are three ways to control the start of the rumor:

1) Single source: Press the SETUP-ONE button. This starts the rumor at one point in the center of the screen.
2) Random source: Press the SETUP-RANDOM button with the INIT-CLIQUE slider set greater than 0. This "seeds" the rumor randomly by choosing a percentage of the population that knows the rumor initially.  This percentage is set using the INIT-CLIQUE slider.
3) Choose source with mouse: Press either SETUP-ONE or SETUP-RANDOM, then press the SPREAD-RUMOR-WITH-MOUSE button.  While this button is down, clicking the mouse button on a patch in the graphics window will tell the rumor to that patch.  

To run the model, you can either "step" through each time step using the STEP button or allow the model to simply run continuously using the GO button.  The model will stop when everyone in the population knows the rumor.

There are three plot windows associated with this rumor model. 

RUMOR SPREAD - plots the percentage of people who know the rumor at each time step.
SUCCESSIVE DIFFERENCES - plots the number of new people who are hearing the rumor at each time step.
SUCCESSIVE RATIOS - plots the percentage of new people who are hearing the rumor at each time step.

The monitor CLIQUE% is the percentage of the patches that have heard the rumor.

The three coloring buttons to the right of the graphics window give you topographic maps of the screen.  The COLOR: WHEN HEARD button colors the screen different shades of YELLOW according to the first time that location heard the rumor.  The COLOR: TIMES HEARD button colors the screen different shades of GREEN according to the number of times that location has heard the rumor.


THINGS TO NOTICE
----------------
The most interesting models to run are those where only a small number of individuals who initially know the rumor.  Use the SPREAD-RUMOR-WITH-MOUSE button to make an initial setup where only three or four patches know the rumor, and all of these patches are in the left half of the graphics window.  Run your model once with "Wrap" off and then again with "Wrap" on.  notice the difference in how the rumor is spread.  Which version seems more realistic to you?

Similarly, run the same model in eight-mode and then in four-mode.  Before you run the model, try to decide, will this make a difference in the spread of the rumor?  Why or why not?

An interesting thing to notice about the spread of the rumor is that the "speed" with which the rumor spreads slows down as more and more people know the rumor.  Why is that?  How is that related to the number of "repeated" or "wasted" tellings of the rumor?  How do the two "differences" plot windows help you to understand the dynamics of the rumor spread?


THINGS TO TRY
-------------
Use SPREAD-RUMOR-WITH-MOUSE to place four "seeds" for the rumor centered in each of the four quadrants of the grid.  Notice the pattern of "repeated tellings."  Move the four "seeds" closer into the center of the grid.  How does the pattern or "repeated tellings" change?  Move the "seeds" away from the center of the grid.  How does the pattern of repeated tellings change?  How will it change if  you turn "wrap" on or off?

Explore other patterns of seeding the rumor and its impact on the pattern of repeated tellings.


EXTENDING THE MODEL
-------------------
Here are some suggestions for ways to extend the model.

- Introduce physical barriers into the simulation.  These spatial barriers would be obstacles around which the rumor would have to spread.  One could imagine a room where there was only a one cell entry.  How long would it take to reach the entire population in this case?  And how would that curve (the function of the number of people who know the rumor versus time) compare to the spread of the rumor when there was no such barrier?

- Assign a probability with which the rumor is told.  In the current model, each time a person meets his/her neighbor, s/he tells the neighbor the rumor.  How would the spread of the rumor change if the telling of the rumor took place only 50% of the time? or 30% of the time?

- Can you make a rumor model that does not spread the rumor through spatial proximity?


NETLOGO FEATURES
----------------
Note the use of the "neighbors" and "neighbors4" primitives to implement 8-mode and 4-mode, respectively.


RELATED MODELS
--------------
Virus, AIDS


CREDITS AND REFERENCES
----------------------
This model is itself an extension of a physical experiment where spatial proximity was not a factor in the spread of the rumor.  Contact Helen M. Doerr at hmdoerr@syr.edu regarding papers in preparation.  Thanks to Dr. Doerr for inspiration for this model.

To refer to this model in academic publications, please use: Wilensky, U. (1998).  NetLogo Rumor Mill model. http://ccl.northwestern.edu/netlogo/models/RumorMill. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

In other publications, please use: Copyright 1998 by Uri Wilensky.  All rights reserved.  See http://ccl.northwestern.edu/netlogo/models/RumorMill for terms of use.
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NetLogo 2.0beta5
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