# Preferential Attachment, Homophily etc. Networks

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turtles-own [wealth my-probability-of-homophily] globals[number-homophily number-contagion flag] extensions[nw] to setup clear-all nw:set-context turtles links ask patches [set pcolor white] create-turtles number-of-nodes [ set wealth Random 20 set shape "circle" set color scale-color green wealth -5 25 set size 1 setxy random-xcor random-ycor set my-probability-of-homophily random probability-of-homophily] reset-ticks end to go ask links [set color gray] ask one-of turtles [ make-node-homophily find-partner wealth] ; if number-homophily >= number-of-links [ask links [set color gray] ask one-of turtles [set color red] stop] tick if layout? [layout] end to contagion set flag 0 if any? turtles with [color != red and count link-neighbors > 0] [ ask turtles with [color = red] [ ask link-neighbors [if random 100 <= probability-linked-affected [set color red set flag 1] ask other turtles [ if random 100 < probability-other-affected [set color red set flag 1]] ] ] if flag = 1 [set number-contagion number-contagion + 1] ] end to make-node-homophily [node] if node != nobody [ create-link-with node [set color red] move-to node fd 8 ] set number-homophily number-homophily + 1 end to-report find-partner [W] ifelse random 100 < my-probability-of-homophily [report one-of other turtles with [wealth = W or wealth = W - 1 or wealth = W + 1]] [report one-of other turtles with [wealth > W]] end ;;;;;;;;;;;;;; ;;; Layout ;;; ;;;;;;;;;;;;;; ;; resize-nodes, change back and forth from size based on degree to a size of 1 to resize-nodes ifelse all? turtles [size <= 1] [ ;; a node is a circle with diameter determined by ;; the SIZE variable; using SQRT makes the circle's ;; area proportional to its degree ask turtles [ set size sqrt sqrt count link-neighbors ] ] [ ask turtles [ set size 1 ] ] end to layout ;; the number 3 here is arbitrary; more repetitions slows down the ;; model, but too few gives poor layouts repeat 3 [ ;; the more turtles we have to fit into the same amount of space, ;; the smaller the inputs to layout-spring we'll need to use let factor sqrt count turtles ;; numbers here are arbitrarily chosen for pleasing appearance layout-spring turtles links (1 / factor) (10 / factor) (10 / factor) display ;; for smooth animation ] ;; don't bump the edges of the world let x-offset max [xcor] of turtles + min [xcor] of turtles let y-offset max [ycor] of turtles + min [ycor] of turtles ;; big jumps look funny, so only adjust a little each time set x-offset limit-magnitude x-offset 0.1 set y-offset limit-magnitude y-offset 0.1 ask turtles [ setxy (xcor - x-offset / 2) (ycor - y-offset / 2) ] end to-report limit-magnitude [number limit] if number > limit [ report limit ] if number < (- limit) [ report (- limit) ] report number end

There is only one version of this model, created about 9 years ago by Jiawei Fu.

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