;; text, like this, that start with semi-colons are comments and do not effect anything ;; ;; First we have lists of general and individual properties/slots globals [global-sales] breed [sellers seller] breed [buyers buyer] ;; only attribute is age, all agents automatically have the attribute of color and size sellers-own [money food price sales] buyers-own [money food] ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Next we have the procedure to initialise the simulation ;; this is executed when one presses the "setup" button to setup clear-all ;; this clears everything at the start - a clean slate ;; first create the sellers people, shown as circles, put them on a random patch ;; the parameter "population" is determined by a slider create-sellers number-sellers [ ;; set initial characteristics set money random 500 set food random 100 ;; random price to start with set price 5 + random 10 ;; set appearence set shape "truck" set size food / 500 set xcor 0 + random-normal 0 0.15 set ycor random-float 1 ] ;; do the same for the buyers create-buyers number-buyers [ set money random 20 set food random 10 ;; set appearence set shape "person" set size food / 100 set xcor 1 + random-normal 0 0.15 set ycor random-float 1 ] reset-ticks ;; this initialises the simulation time system and graphs end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Next we have the procedure to progress the simulation one time step ;; this is executed when one presses the "step" button or repeatedly ;; if one presses the "go" button to go let chosen-seller nobody let possible-sellers nobody let desired-amount 0 set global-sales 0 ;; things that happend to all sellers each time period ask sellers [ ;; reset sales counter set sales 0 ;; add to food to sell from production and subtract costs set food food + production-rate set money money - seller-costs ;; kill bankrupt sellers if money < 0 [die] ] ;; things that happen to all buyers each time period ask buyers [ ;; buyers income set money money + buyer-income show (word "Food of " self " is " food) ;; if have enough food, eat some, if none die set food food - usage-rate ;; kill starving buyers if food < 0 [die] ;; find possible sellers set possible-sellers sellers with [food >= 1] if any? possible-sellers [ ;; find seller with lowest price set chosen-seller min-one-of possible-sellers [price] ;; determine how many units could buy from this seller set desired-amount floor (money / ([price] of chosen-seller)) ;; if can buy one unit or more buy it, adjust food and money if desired-amount >= 1 [ set food food + desired-amount set money money - desired-amount * [price] of chosen-seller ;; adjust food and money for seller ask chosen-seller [ set food food - desired-amount set money money + desired-amount * [price] of chosen-seller ;; record sales set sales sales + desired-amount set global-sales global-sales + sales ] ] ] ] ;; how sellers change their price ask sellers [ if sales < 3 [set price price * 0.75] if sales > 6 [set price price / 0.75] ] ;; adjust the size of icons depending upon their stock of food ask sellers [ set size food / 500] ask buyers [ set size food / 100] tick ;; this progresses the tick counter by one end @#$#@#$#@ GRAPHICS-WINDOW 210 10 651 472 -1 -1 215.5 1 10 1 1 1 0 1 1 1 0 1 0 1 0 0 1 ticks 30.0 BUTTON 5 10 72 43 NIL setup NIL 1 T OBSERVER NIL NIL NIL NIL 1 BUTTON 76 10 139 43 step go NIL 1 T OBSERVER NIL NIL NIL NIL 1 SLIDER 17 57 189 90 number-sellers number-sellers 0 10 5 1 1 NIL HORIZONTAL SLIDER 17 212 189 245 number-buyers number-buyers 0 100 100 1 1 NIL HORIZONTAL SLIDER 17 130 189 163 production-rate production-rate 0 100 11 1 1 NIL HORIZONTAL SLIDER 17 284 189 317 usage-rate usage-rate 0 10 1 1 1 NIL HORIZONTAL SLIDER 17 248 189 281 buyer-income buyer-income 0 10 10 1 1 NIL HORIZONTAL SLIDER 17 94 189 127 seller-costs seller-costs 0 100 50 1 1 NIL HORIZONTAL BUTTON 143 10 207 44 NIL go T 1 T OBSERVER NIL NIL NIL NIL 1 MONITOR 8 423 77 468 Tot.Sales global-sales 1 1 11 MONITOR 113 325 206 370 Av. Buyer Food mean [food] of buyers 0 1 11 MONITOR 112 373 206 418 Av.Seller Food mean [food] of sellers 0 1 11 MONITOR 83 424 146 469 Av.Price mean [price] of sellers 1 1 11 MONITOR 13 326 110 371 Av.Buyer Money mean [money] of buyers 1 1 11 MONITOR 12 374 109 419 Av.Seller Money mean [money] of sellers 1 1 11 PLOT 657 10 857 160 Buyer Food NIL NIL -20.0 20.0 0.0 10.0 true false "" "" PENS "default" 1.0 1 -16777216 true "" "histogram [food] of buyers" PLOT 658 165 858 315 Seller Prices NIL NIL 0.0 50.0 0.0 10.0 true false "" "" PENS "default" 1.0 1 -16777216 true "" "histogram [price] of sellers" PLOT 659 317 859 467 Statistics NIL NIL 0.0 10.0 0.0 10.0 true false "" "" PENS "price" 1.0 0 -16777216 true "" "plot mean [price] of sellers" "sales" 1.0 0 -2674135 true "" "plot mean [sales] of sellers" @#$#@#$#@ ## WHAT IS IT? This is an example model, used as part of the "2-day Introduction to Agent-Based Modelling". This is a simple agent-based market for food with buyers and sellers. Buyers use a given amount of food each time unit, sellers produce different amounts of food. Buyers have an income with which to buy food, sellers have a certain level of costs that they have each time unit. ## HOW IT WORKS There are two dynamic processes. Buyers try to spend what money they have on food each time. If there are any buyers with a unit of food, they choose the one with the minimum price and buy what units of food they can afford from them. Sellers keep track of the number of units they sell, if they sell less than 3 they lower their price, if they sell more than six they raise it. ## HOW TO USE IT Press... "setup" to initialise the simulation "step" to progress the simulation one step "go" to repreatedly step through the simulation ## THINGS TO NOTICE It is very difficult to balance such a market. ## THINGS TO TRY Try to find the conditions that allow for a stable market to develop. ## EXTENDING THE MODEL Think about the decision from the point of view of the buyers and sellers (each). What limitations would they have? What aspects of their environment might they know about? What additional factors might they use in their decision making? How might they realistically make their decisions? ## NETLOGO FEATURES Note the use of local variables within the "go" procedure. They are declared using "let". ## CREDITS AND REFERENCES Model by Bruce Edmonds, Feb 2013 http://cfpm.org/simulationcourse @#$#@#$#@ default true 0 Polygon -7500403 true true 150 5 40 250 150 205 260 250 airplane true 0 Polygon -7500403 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15 arrow true 0 Polygon -7500403 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150 box false 0 Polygon -7500403 true true 150 285 285 225 285 75 150 135 Polygon -7500403 true true 150 135 15 75 150 15 285 75 Polygon -7500403 true true 15 75 15 225 150 285 150 135 Line -16777216 false 150 285 150 135 Line -16777216 false 150 135 15 75 Line -16777216 false 150 135 285 75 bug true 0 Circle -7500403 true true 96 182 108 Circle -7500403 true true 110 127 80 Circle -7500403 true true 110 75 80 Line -7500403 true 150 100 80 30 Line -7500403 true 150 100 220 30 butterfly true 0 Polygon -7500403 true true 150 165 209 199 225 225 225 255 195 270 165 255 150 240 Polygon -7500403 true true 150 165 89 198 75 225 75 255 105 270 135 255 150 240 Polygon -7500403 true true 139 148 100 105 55 90 25 90 10 105 10 135 25 180 40 195 85 194 139 163 Polygon -7500403 true true 162 150 200 105 245 90 275 90 290 105 290 135 275 180 260 195 215 195 162 165 Polygon -16777216 true false 150 255 135 225 120 150 135 120 150 105 165 120 180 150 165 225 Circle -16777216 true false 135 90 30 Line -16777216 false 150 105 195 60 Line -16777216 false 150 105 105 60 car false 0 Polygon -7500403 true true 300 180 279 164 261 144 240 135 226 132 213 106 203 84 185 63 159 50 135 50 75 60 0 150 0 165 0 225 300 225 300 180 Circle -16777216 true false 180 180 90 Circle -16777216 true false 30 180 90 Polygon -16777216 true false 162 80 132 78 134 135 209 135 194 105 189 96 180 89 Circle -7500403 true true 47 195 58 Circle -7500403 true true 195 195 58 circle false 0 Circle -7500403 true true 0 0 300 circle 2 false 0 Circle -7500403 true true 0 0 300 Circle -16777216 true false 30 30 240 cow false 0 Polygon -7500403 true true 200 193 197 249 179 249 177 196 166 187 140 189 93 191 78 179 72 211 49 209 48 181 37 149 25 120 25 89 45 72 103 84 179 75 198 76 252 64 272 81 293 103 285 121 255 121 242 118 224 167 Polygon -7500403 true true 73 210 86 251 62 249 48 208 Polygon -7500403 true true 25 114 16 195 9 204 23 213 25 200 39 123 cylinder false 0 Circle -7500403 true true 0 0 300 dot false 0 Circle -7500403 true true 90 90 120 face happy false 0 Circle -7500403 true true 8 8 285 Circle -16777216 true false 60 75 60 Circle -16777216 true false 180 75 60 Polygon -16777216 true false 150 255 90 239 62 213 47 191 67 179 90 203 109 218 150 225 192 218 210 203 227 181 251 194 236 217 212 240 face neutral false 0 Circle -7500403 true true 8 7 285 Circle -16777216 true false 60 75 60 Circle -16777216 true false 180 75 60 Rectangle -16777216 true false 60 195 240 225 face sad false 0 Circle -7500403 true true 8 8 285 Circle -16777216 true false 60 75 60 Circle -16777216 true false 180 75 60 Polygon -16777216 true false 150 168 90 184 62 210 47 232 67 244 90 220 109 205 150 198 192 205 210 220 227 242 251 229 236 206 212 183 fish false 0 Polygon -1 true false 44 131 21 87 15 86 0 120 15 150 0 180 13 214 20 212 45 166 Polygon -1 true false 135 195 119 235 95 218 76 210 46 204 60 165 Polygon -1 true false 75 45 83 77 71 103 86 114 166 78 135 60 Polygon -7500403 true true 30 136 151 77 226 81 280 119 292 146 292 160 287 170 270 195 195 210 151 212 30 166 Circle -16777216 true false 215 106 30 flag false 0 Rectangle -7500403 true true 60 15 75 300 Polygon -7500403 true true 90 150 270 90 90 30 Line -7500403 true 75 135 90 135 Line -7500403 true 75 45 90 45 flower false 0 Polygon -10899396 true false 135 120 165 165 180 210 180 240 150 300 165 300 195 240 195 195 165 135 Circle -7500403 true true 85 132 38 Circle -7500403 true true 130 147 38 Circle -7500403 true true 192 85 38 Circle -7500403 true true 85 40 38 Circle -7500403 true true 177 40 38 Circle -7500403 true true 177 132 38 Circle -7500403 true true 70 85 38 Circle -7500403 true true 130 25 38 Circle -7500403 true true 96 51 108 Circle -16777216 true false 113 68 74 Polygon -10899396 true false 189 233 219 188 249 173 279 188 234 218 Polygon -10899396 true false 180 255 150 210 105 210 75 240 135 240 house false 0 Rectangle -7500403 true true 45 120 255 285 Rectangle -16777216 true false 120 210 180 285 Polygon -7500403 true true 15 120 150 15 285 120 Line -16777216 false 30 120 270 120 leaf false 0 Polygon -7500403 true true 150 210 135 195 120 210 60 210 30 195 60 180 60 165 15 135 30 120 15 105 40 104 45 90 60 90 90 105 105 120 120 120 105 60 120 60 135 30 150 15 165 30 180 60 195 60 180 120 195 120 210 105 240 90 255 90 263 104 285 105 270 120 285 135 240 165 240 180 270 195 240 210 180 210 165 195 Polygon -7500403 true true 135 195 135 240 120 255 105 255 105 285 135 285 165 240 165 195 line true 0 Line -7500403 true 150 0 150 300 line half true 0 Line -7500403 true 150 0 150 150 pentagon false 0 Polygon -7500403 true true 150 15 15 120 60 285 240 285 285 120 person false 0 Circle -7500403 true true 110 5 80 Polygon -7500403 true true 105 90 120 195 90 285 105 300 135 300 150 225 165 300 195 300 210 285 180 195 195 90 Rectangle -7500403 true true 127 79 172 94 Polygon -7500403 true true 195 90 240 150 225 180 165 105 Polygon -7500403 true true 105 90 60 150 75 180 135 105 plant false 0 Rectangle -7500403 true true 135 90 165 300 Polygon -7500403 true true 135 255 90 210 45 195 75 255 135 285 Polygon -7500403 true true 165 255 210 210 255 195 225 255 165 285 Polygon -7500403 true true 135 180 90 135 45 120 75 180 135 210 Polygon -7500403 true true 165 180 165 210 225 180 255 120 210 135 Polygon -7500403 true true 135 105 90 60 45 45 75 105 135 135 Polygon -7500403 true true 165 105 165 135 225 105 255 45 210 60 Polygon -7500403 true true 135 90 120 45 150 15 180 45 165 90 sheep false 0 Rectangle -7500403 true true 151 225 180 285 Rectangle -7500403 true true 47 225 75 285 Rectangle -7500403 true true 15 75 210 225 Circle -7500403 true true 135 75 150 Circle -16777216 true false 165 76 116 square false 0 Rectangle -7500403 true true 30 30 270 270 square 2 false 0 Rectangle -7500403 true true 30 30 270 270 Rectangle -16777216 true false 60 60 240 240 star false 0 Polygon -7500403 true true 151 1 185 108 298 108 207 175 242 282 151 216 59 282 94 175 3 108 116 108 target false 0 Circle -7500403 true true 0 0 300 Circle -16777216 true false 30 30 240 Circle -7500403 true true 60 60 180 Circle -16777216 true false 90 90 120 Circle -7500403 true true 120 120 60 tree false 0 Circle -7500403 true true 118 3 94 Rectangle -6459832 true false 120 195 180 300 Circle -7500403 true true 65 21 108 Circle -7500403 true true 116 41 127 Circle -7500403 true true 45 90 120 Circle -7500403 true true 104 74 152 triangle false 0 Polygon -7500403 true true 150 30 15 255 285 255 triangle 2 false 0 Polygon -7500403 true true 150 30 15 255 285 255 Polygon -16777216 true false 151 99 225 223 75 224 truck false 0 Rectangle -7500403 true true 4 45 195 187 Polygon -7500403 true true 296 193 296 150 259 134 244 104 208 104 207 194 Rectangle -1 true false 195 60 195 105 Polygon -16777216 true false 238 112 252 141 219 141 218 112 Circle -16777216 true false 234 174 42 Rectangle -7500403 true true 181 185 214 194 Circle -16777216 true false 144 174 42 Circle -16777216 true false 24 174 42 Circle -7500403 false true 24 174 42 Circle -7500403 false true 144 174 42 Circle -7500403 false true 234 174 42 turtle true 0 Polygon -10899396 true false 215 204 240 233 246 254 228 266 215 252 193 210 Polygon -10899396 true false 195 90 225 75 245 75 260 89 269 108 261 124 240 105 225 105 210 105 Polygon -10899396 true false 105 90 75 75 55 75 40 89 31 108 39 124 60 105 75 105 90 105 Polygon -10899396 true false 132 85 134 64 107 51 108 17 150 2 192 18 192 52 169 65 172 87 Polygon -10899396 true false 85 204 60 233 54 254 72 266 85 252 107 210 Polygon -7500403 true true 119 75 179 75 209 101 224 135 220 225 175 261 128 261 81 224 74 135 88 99 wheel false 0 Circle -7500403 true true 3 3 294 Circle -16777216 true false 30 30 240 Line -7500403 true 150 285 150 15 Line -7500403 true 15 150 285 150 Circle -7500403 true true 120 120 60 Line -7500403 true 216 40 79 269 Line -7500403 true 40 84 269 221 Line -7500403 true 40 216 269 79 Line -7500403 true 84 40 221 269 wolf false 0 Polygon -7500403 true true 135 285 195 285 270 90 30 90 105 285 Polygon -7500403 true true 270 90 225 15 180 90 Polygon -7500403 true true 30 90 75 15 120 90 Circle -1 true false 183 138 24 Circle -1 true false 93 138 24 x false 0 Polygon -7500403 true true 270 75 225 30 30 225 75 270 Polygon -7500403 true true 30 75 75 30 270 225 225 270 @#$#@#$#@ NetLogo 5.0.1 @#$#@#$#@ @#$#@#$#@ @#$#@#$#@ @#$#@#$#@ @#$#@#$#@ default 0.0 -0.2 0 1.0 0.0 0.0 1 1.0 0.0 0.2 0 1.0 0.0 link direction true 0 Line -7500403 true 150 150 90 180 Line -7500403 true 150 150 210 180 @#$#@#$#@ 0 @#$#@#$#@