# Civ

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patches-own [water] globals [people-constant water-constant] to setup clear-all draw-terrain crt population [ set color orange set size 2 set shape "person" ; distribute randomly, making sure none of them are in the water setxy random-xcor random-ycor while [water = true] [ setxy random-xcor random-ycor ] ] set people-constant 0.0 let counter 1 while [counter <= population] [ set people-constant (people-constant + (1.0 / counter)) set counter (counter + 1) ] ; we don't want to count ourselves set people-constant (people-constant - 1) reset-ticks end ;; draw a fixed terrain to draw-terrain ask patches [ set pcolor 72 ; green set water false ] ; ocean along the top ask patches with [pycor > 70] [ set pcolor blue set water true ] ; ocean along the bottom ask patches with [pycor < 3] [ set pcolor blue set water true ] ; lake on the left ask patches with [distancexy 25 30 < 13] [ set pcolor blue set water true ] ; another lake on the right ask patches with [distancexy 70 45 < 10] [ set pcolor blue set water true ] ; river going down from the second lake ask patches with [pxcor > 67 and pxcor < 73 and pycor < 45] [ set pcolor blue set water true ] end to go ask turtles [ ;; the default probability of staying at the current ;; patch derives from laziness let p ((laziness / 100.0) + (get-happiness-adjustment xcor ycor)) let r (random-float 1) ifelse (r > p) [ move-intelligently ] [ set r (random 100) if (impulsiveness > r) [ move-randomly ] ] ] tick end ;; calculate the people index, which we model to have decreasing ;; marginal utility. we go with a harmonic sum as a rough ;; approximation, i.e. the nth neighbor adds value 1/n to-report get-people-index [x y] let people-index 0.0 let people-count 0 ask turtles with [(distancexy x y) < sphere-of-activity] [ set people-count (people-count + 1) set people-index people-index + (1.0 / people-count) ] ;; we counted ourselves in the above, so take it back out set people-index (people-index - 1) ;; normalize the people-index against the maximum possible value ;; that occurs when everyone is all in the same place. after ;; this, people-index will be a number between 0 and 1. set people-index (people-index / people-constant) report people-index end ;; calculate the water index, which we model to have a sharply ;; decreasing marginal utility. we go with the nth neighboring ;; water patch adding value 1/n^2 to-report get-water-index [x y] let water-index 0.0 let water-count 0 ask patches with [(distancexy x y) < sphere-of-activity] [ if (water = true) [ set water-count (water-count + 1) set water-index water-index + (1.0 / (water-count * water-count)) ] ] ;; normalize the water-index against the maximum possible value ;; after this, water-index will be a number between 0 and 1 set water-index (water-index / 1.65) report water-index end ;; reports the probability adjustment of staying, as influenced ;; by being close to water and people. to-report get-happiness-adjustment [x y] let people-index (get-people-index x y) let water-index (get-water-index x y) ;; we define leeway to be the amount of influence either proximity ;; to water or proximity to people can have, and we give these ;; equal parts of the remaining probability. for example, ;; if the default probability of staying is 40%, then we allow ;; each of these two factors to increase the probability by up to ;; 30%, so that if both of them were to be maxed out, and the person ;; had 100% affinity to both, then the probability ;; of staying would be 100%. let leeway ((100.0 - laziness) / 200.0) report (people-index * (affinity-to-people / 100.0) * leeway) + (water-index * (affinity-to-water / 100.0) * leeway) end ;; checks the up/down/left/right squares and moves to the ;; one that makes you the happiest to move-intelligently let x xcor let y ycor ; adjustments in the four directions let adj1 -1 let adj2 -1 let adj3 -1 let adj4 -1 ;; up, idx = 1 set ycor (y + 1) if (water = false) [ set adj1 (get-happiness-adjustment xcor ycor) ] ;; down, idx = 2 set ycor (y - 1) if (water = false) [ set adj2 (get-happiness-adjustment xcor ycor) ] ;; left, idx = 3 set ycor y set xcor (x - 1) if (water = false) [ set adj3 (get-happiness-adjustment xcor ycor) ] ;; left, idx = 4 set xcor (x + 1) if (water = false) [ set adj4 (get-happiness-adjustment xcor ycor) ] ;; figure out what the max adjustment is, and how many ;; of the four directions tie for max let max-adj adj1 let max-count 1 if (adj2 = adj1) [ set max-count (max-count + 1) ] if (adj2 > adj1) [ set max-adj adj2 set max-count 1 ] if (adj3 = adj2) [ set max-count (max-count + 1) ] if (adj3 > adj2) [ set max-adj adj3 set max-count 1 ] if (adj4 = adj3) [ set max-count (max-count + 1) ] if (adj4 > adj3) [ set max-adj adj4 set max-count 1 ] ;; now, randomly choose one of the directions that tie for ;; the max adjustment let max-idx (random max-count) if (adj1 = max-adj) [ if (max-idx = 0) [ set xcor x set ycor (y + 1) stop ] set max-idx (max-idx - 1) ] if (adj2 = max-adj) [ if (max-idx = 0) [ set xcor x set ycor (y - 1) stop ] set max-idx (max-idx - 1) ] if (adj3 = max-adj) [ if (max-idx = 0) [ set xcor (x - 1) set ycor y stop ] set max-idx (max-idx - 1) ] if (adj4 = max-adj) [ if (max-idx = 0) [ set xcor (x + 1) set ycor y stop ] set max-idx (max-idx - 1) ] end to move-randomly let legal-move false let r 0 while [legal-move = false] [ set r (random 360) rt r fd 1 ifelse (water = true) [ set legal-move false bk 1 lt r ] [ set legal-move true ] ] end

There is only one version of this model, created almost 12 years ago by Kay Ramey.

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