;; globals [ gv-scribe gv-attractor tb-zones cn-days ] breed [mechanisms a-mach] breed [entities a-so] breed [exceptions an-exch] ; patches-own [dm-zone] mechanisms-own [mt-andon dm-lane] entities-own [dm-arrival dm-purchase dm-demand dm-sales dm-shortage dm-devol dm-revenue dm-expenses dm-profit] ; to setup clear-all set cn-days 0 set-default-shape exceptions "bug" set-default-shape entities "box" set-default-shape mechanisms "circle" set tb-zones (list "exch" "sink" "shortage" "devol" "source" ) ask patches [ set pcolor gray] ask patches with [12 < pycor] [ set pcolor brown set dm-zone "exch"] ask patches with [12 < pxcor] [ set pcolor cyan set dm-zone "sink"] ask patches with [dm-zone = "sink" and -10 < pycor] [set dm-zone "shortage" set pcolor pink - 2] ask patches with [dm-zone = "shortage" and 4 < pycor] [set dm-zone "devol" set pcolor yellow - 2 ] ask patches with [pxcor < -12] [ set pcolor lime set dm-zone "source"] ask patch 0 0 [ set pcolor turquoise sprout-mechanisms 1 [mt-create-scribe] ] ask one-of patches with ["source" = dm-zone] [ sprout-entities 1 [set label "SO" show (word label " created to prevent failure in plot... to be destroyed later on.")] ] show (word " ------------------------ a new experiment starts ... ------------------------") foreach tb-zones [ ask one-of patches with [? = dm-zone] [set plabel dm-zone] ] reset-ticks end ;; to go carefully [ if any? exceptions [error (word " there are bugs in the system!" )] ask entities-on patches with [ dm-zone = "source"] [if label = "SO" [die] ] ask gv-scribe [run mt-andon] ] [ eh-catch "go" error-message clear-ticks stop ] tick-advance 0.25 end ;; to eh-catch [#where #what] show (word ticks " PANIC! ----------------------> E X C E P T I O N caught: " #what " at :" #where) ask one-of patches with [dm-zone = "exch"] [ sprout-exceptions 1 [set color violet set label #what] ] end ;; to mt-create-scribe set label "scribe" set color blue set size 3 set mt-andon task mt-arrival ask patch-here [set dm-zone "blocked"] ask neighbors [set dm-zone "blocked" set pcolor orange] let lv-sink (list "sink" "shortage" "devol") set dm-lane patches with [( 1 < pxcor) and (0 = pycor) and (not member? dm-zone lv-sink)] ask dm-lane [set pcolor gray - 2 set dm-zone [label] of myself ] ask patch-at (1 + max [pxcor] of dm-lane) 0 [set pcolor blue set dm-zone "attractor" set gv-attractor self] show (word label " will represent Freddie ...") set gv-scribe self end ;; to mt-arrival carefully [ set mt-andon task mt-demand ask one-of patches with [dm-zone = "source"] [ sprout-entities 1 [ set color blue set label "PO" set dm-arrival ticks set dm-purchase pa-purchase set dm-expenses (dm-purchase * bu-po-price) create-link-to gv-scribe [set color turquoise stamp] if bu-debug-mode? [show (word ticks " DEBUG! " label " daily order starts its trajectory ...Freddie buys " dm-purchase " newspapers.") ] ] ] ] [eh-catch "arrival" error-message] end ;; to mt-demand carefully [ set mt-andon task mt-sales let lv-wip entities with ["PO" = label] if count lv-wip != 1 [error (word " only one WIP entity is expected; count " count lv-wip)] ask lv-wip [ set label "demand" set color violet face gv-scribe move-to gv-scribe move-to one-of neighbors set dm-demand rpt-demand if bu-debug-mode? [show (word ticks " DEBUG! " label " today's demand is " dm-demand)] ] ] [eh-catch "demand" error-message] end ;; to mt-sales carefully [ set mt-andon task mt-record let lv-wip entities with ["demand" = label] if count lv-wip != 1 [error (word " only one WIP entity is expected; count " count lv-wip)] ask entities-on dm-lane [mt-flow-so] ask lv-wip [ set label "SO" set color green move-to min-one-of [dm-lane] of myself [pxcor] set dm-sales min (list dm-demand dm-purchase) set dm-shortage dm-demand - dm-sales if 0 < dm-shortage [set color red] set dm-devol dm-purchase - dm-sales if 0 < dm-devol [set color yellow] set dm-revenue (dm-sales * bu-so-price) + (dm-devol * bu-devol-price) set dm-profit dm-revenue - dm-expenses show (word ticks " INFO! " label " demand " dm-demand " PO :" dm-purchase " SO:" dm-sales " shortage:" dm-shortage " devol :" dm-devol " profit:" dm-profit) if (0 < dm-devol) and (0 < dm-shortage) [error (word " devol & shortage can not happen both in the same day.")] if (dm-devol < 0 ) or (dm-shortage < 0) [error (word " devol and shortage can NOT be negative any of them.")] ] ] [eh-catch "sales" error-message] end ;; to mt-record carefully [ set mt-andon task mt-arrival let lv-wip entities with ["H" = label] if bu-debug-mode? [show (word ticks " DEBUG! " label " historian count:" count lv-wip )] set cn-days 1 + cn-days if 1 < abs (int cn-days - ticks) [error (word " the tick advance is not synchonized properly ...")] update-plots while [bu-historian-size < count entities with ["H" = label] ] [ ask min-one-of entities with ["H" = label] [dm-arrival] [ if bu-debug-mode? [show (word ticks " DEBUG!" label " applying 5S policy to erase oldest entity.")] die ] ] ] [eh-catch "record" error-message] end ;; to mt-flow-so set label "H" let sv-zone [dm-zone] of patch-here face gv-attractor fd 1 if [dm-zone] of patch-here != sv-zone [ if bu-debug-mode? [show (word " DEBUG! zone before " sv-zone " zone now " [dm-zone] of patch-here " sent to sink!") ] move-to one-of patches with ["sink" = dm-zone] if 0 < dm-shortage [move-to one-of patches with ["shortage" = dm-zone] ] if 0 < dm-devol [move-to one-of patches with ["devol" = dm-zone] ] ask my-out-links [stamp-erase die] ] end ;; to-report rpt-demand let lv-demand (40 + random 31) report lv-demand end ;; @#$#@#$#@ GRAPHICS-WINDOW 229 10 720 548 18 19 13.0 1 10 1 1 1 0 0 0 1 -18 18 -19 19 1 1 1 DAY# 30.0 BUTTON 35 33 101 66 setup setup NIL 1 T OBSERVER NIL NIL NIL NIL 1 BUTTON 109 95 194 128 go once go NIL 1 T OBSERVER NIL NIL NIL NIL 0 SLIDER 16 175 188 208 pa-purchase pa-purchase 35 85 57 1 1 pcs HORIZONTAL TEXTBOX 739 36 1066 55 Freddie's newsstand - see INFO tab. 18 115.0 1 BUTTON 32 95 95 128 go go T 1 T OBSERVER NIL NIL NIL NIL 0 TEXTBOX 19 227 169 255 Analisis de sensibilidad. (parms) 11 44.0 1 TEXTBOX 19 151 169 169 Espacio del decisor. 11 105.0 1 SLIDER 20 274 192 307 bu-po-price bu-po-price 1.0 2.5 1.5 0.1 1 $ HORIZONTAL MONITOR 744 74 852 119 num days gone cn-days 0 1 11 SWITCH 19 331 185 364 bu-debug-mode? bu-debug-mode? 1 1 -1000 PLOT 747 137 1331 287 plot CCA NIL NIL 0.0 10.0 0.0 10.0 true true "" "" PENS "demand" 1.0 0 -5825686 true "" "plot [dm-demand] of one-of entities with [label = \"SO\"]" "sales" 1.0 0 -14439633 true "" "plot [dm-sales] of one-of entities with [label = \"SO\"]" "shortage" 1.0 0 -5298144 true "" "plot [dm-shortage] of one-of entities with [label = \"SO\"]" "devol" 1.0 0 -9276814 true "" "plot [dm-devol] of one-of entities with [label = \"SO\"]" SLIDER 24 386 196 419 bu-so-price bu-so-price 1 3.0 2.5 0.1 1 $ HORIZONTAL SLIDER 26 438 198 471 bu-devol-price bu-devol-price 0 2.5 0.5 0.1 1 $ HORIZONTAL PLOT 753 306 953 456 demand histogram NIL NIL 35.0 85.0 0.0 10.0 true false "" "" PENS "demand" 1.0 1 -5825686 true "" "histogram [dm-demand] of entities with [\"H\" = label]" PLOT 1134 302 1334 452 profit histogram NIL NIL -20.0 120.0 0.0 10.0 true false "" "" PENS "profit" 1.0 1 -13345367 true "" "histogram [dm-profit] of entities with [\"H\" = label]" MONITOR 984 317 1069 362 mean profit mean [dm-profit] of entities with [\"H\" = label] 1 1 11 SLIDER 11 488 204 521 bu-historian-size bu-historian-size 250 3500 850 150 1 entities HORIZONTAL MONITOR 986 384 1082 429 historian size count entities with [\"H\" = label] 0 1 11 @#$#@#$#@ ## WHAT IS IT? AN INVENTORY MANAGEMENT EXAMPLE. One of the daily neswpaper that Freddie sells from his newsstand is the "Financial XYZ". A distributor brings the day's copies of the Financial XYZ to the newsstand early in the morning. Any copies unsold at the end of the day are returned to the distributor the next morning. However, to encourage ordering a large number of copies, the distributor does give a small refund for unsold copies. Here are the Freddie's cost figures: Freddie pays $1.50 per copy delivered. Freddie sells at $2.50 per copy. Freddie's refund is $0.50 per unsold copy. Partially because of the refund, Freddie has always taken a plentiful supply. However, he has become concerned about paying so much for copies that then have to be returned unsold, particularly since this has been ocurring nearly every day. To investigate this further, he has compiled the following record of his daily demand: Freddie sells anywhere between 40 and 70 copies on any given day. The frequency is distributed uniform (roughly equal each number in between 40 - 70). The decision Freddie neds to make iw the number of copies to order per day from the distributor. His objective is to maximize his average daily profit. ## HOW IT WORKS Freddie is modeled as a mechanism who goes along a cycle of states. One state is to purchase; then simulate the demand for this day; then do the sales; then record the results. One entity traverse the system during each cycle. Each complete cycle makes a day. Next Freddie's cycle, another entity enters the system. Hence, the entity carries the data of what happens in a concrete day. So, we have one entity per day. The user limits the amount of history to be ketp in the system for visibility and calculations. Oldest stuff are removed in order to prevent degradation of the runtime. ## HOW TO USE IT The user sets the slider bars with the parameters of the experiment she wants to run. Then, she presses the setup followed by the go buttom. There is a switch available to set the system verbose (debug mode on). If so, the command center is showing details of what the system is doing. ## THINGS TO NOTICE Plots refresh at the end of the day. The tick advances a fraction of day each time, in order to give Freddie enough ticks to do the complete task of the day. ## THINGS TO TRY Replicate the same experimental conditions to realize variability. Compare short experiments (like 20 days) versus long experiments (like 1,000 days) Experiment situations that you know what the outcome should be. This is key to verify the model. e.g. you knwo that if Freddie buys the minimum demand, 40, the gains will be 40. ## EXTENDING THE MODEL Experiment sensitivity by changing parameters; e.g. the price of the purchase, the sales price, the amount of refunding, ... ## NETLOGO FEATURES Have a look about the cautions taken in order to prevent failures (bugs) in the model. Alter parts of the code so to force exceptions to raise and check whether they are trapped or not. Ask yourself about usability as a quality factor for the end-user. Read critically the job instructions and aids provided by the interface, the info tab, the readibility of the code ... ## RELATED MODELS This problem can be treated as an "stochastic one-period inventory model for perishable products". ## CREDITS AND REFERENCES Hillier-Lieberman. Operations Research. 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