Enhanced Appendices | An Enchantment of Digital Archaeology > Pot Trade Model Code

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Pot Trade Model Code

;; Written in NetLogo 6.0.4 ;; We implement Tom Brughmans’s (2013) simple pot trade model on ;; top of a network created by the code snippet ‘network import ;; example’ ;; Here we have also implemented a ‘breakage’ feature that uses ;; the ‘strength’ value of the network as an indication of the ;; diffi culty of trading pots over a particular route. You might ;; interpret that value as bumpiness of the road, or likelihood ;; of cargoes being lost, etc. ;;---- Things to do in the interface window —— ;; in the interface, create a slider with minimum 0, maximum 1 ;; and set its value to 0.5. Call it trade-threshold ;; in the interface, create a slider with minimum 1, maximum 100 ;; and set its value at 50. Call it num-pots ;; you can create a ‘kill’ button by right-clicking in the ;; interface, selecting button, and putting the code below ;; into its code panel (without the ;; of course): ;; ask one-of links [die] ;; you can add links to the network randomly by making a button ;; with the following code (without the ;; of course): ;; ask one-of turtles [ create-link-to one-of other turtles ;; [set strength random-fl oat 3 ;; set label strength]] ;;— Things to notice — ;; when you run the code, notice how the default network seems to ;; shunt pots to particular nodes; notice how adding links ;; rejigs the way the ‘economy’ of this model works turtles-own [node-id pots] links-own [strength] globals [links-list breakage-factor] ;; we add the global ;; variable ‘breakage-factor’ to enable links and nodes to ;; communicate data to go let total-pots sum [pots] of turtles repeat total-pots [ trade-pots ] let poorturtles turtles with [ pots < 0 ] if any? poorturtles [ ask poorturtles [set pots 1] ] ;; this prevents division errors, ;; but could also represent a kind of cyclical production ask turtles [set size 0.1 + 5 * sqrt (pots / total-pots)] tick end to trade-pots let target one-of turtles with [pots > 0 and count out-linkneighbors > 0] if target != nobody and random-float 1 > trade-threshold ;; target represents one site, one turtle at a time that we want ;; to run our trade routine [ ;; converts the strength of the link to a number the turtles can ;; use ask links [set breakage-factor strength] ask target [ print breakage-factor let pots-loss 1 + breakage-factor set pots max (list 0 (pots - pots-loss)) ;; 1 pot plus the breakage - so we’re treating the strength of ;; the link as a kind of friction, a certain kind of wastage on ;; that route ask one-of out-link-neighbors [set pots pots + 1] ;; no breakage, only the pot arrives ] ] end to import-network clear-all set-default-shape turtles “circle” import-attributes layout-circle (sort turtles) (max-pxcor - 1) import-links reset-ticks ;; New code that we are adding to the import network procedure ask turtles [ set pots random (num-pots) ] end ;; This next procedure reads in a files that contains node- ;; specific ;; attributes ;; including an unique identification number to import-attributes ;; This opens the file, so we can use it. file-open “attributes.txt” ;; Read in all the data in the file ;; data on the line is in this order: ;; node-id attribute1 attribute2 while [not file-at-end?] [ ;; this reads a single line into a three-item list let items read-from-string (word “[“ file-read-line “]”) create-turtles 1 [ set node-id item 0 items set size item 1 items set color item 2 items ] ] file-close end ;; This next procedure reads in a file that contains all the ;; links. The file is simply 3 columns separated by spaces. In ;; this example, the links are directed. The first column ;; contains the node-id of the node originating the link. The ;; second column the node-id of the node on the other end of the ;; link. The third column is the strength of the link. to import-links ;; This opens the file, so we can use it. file-open “links.txt” ;; Read in all the data in the file while [not file-at-end?] [ ;; this reads a single line into a three-item list let items read-from-string (word “[“ file-read-line “]”) ask get-node (item 0 items) [ create-link-to get-node (item 1 items) [ set label item 2 items set strength item 2 items] ; MAR24 added this ] ] file-close end ;; Helper procedure for looking up a node by node-id. to-report get-node [id] report one-of turtles with [node-id = id] end

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