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Algoritmai ir duomenų struktūros ( AD S)

Algoritmai ir duomenų struktūros ( AD S). 6 paskaita Saulius Ragaišis , VU MIF saulius.ragaisis@mif.vu.lt 20 12 - 03 - 12. Modeliavimo programos pavyzdys. Sąlyga : savitarnos parduotuvė dirba T laiko vienetų;

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Algoritmai ir duomenų struktūros ( AD S)

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  1. Algoritmai ir duomenų struktūros(ADS) 6 paskaita Saulius Ragaišis, VU MIF saulius.ragaisis@mif.vu.lt 2012-03-12

  2. Modeliavimo programos pavyzdys Sąlyga:savitarnos parduotuvė dirba T laiko vienetų; joje yra N kasų;kiekvienu laiko momentu su tikimybe M (%) ateina klientas;jo apsipirkimo laikas yra atsitiktinis, bet ne didesnis nei A;baigęs pirkti, jis stoja į eilę prie atsitiktinės kasos;jo aptarnavimo prie kasos laikas yra atsitiktinis, bet ne didesnis nei B.

  3. Modeliavimo programos pavyzdys Rasti:kiek reikia turėti parduotuvės vežimėlių, kad jų nepritrūktų (daroma prielaida, kad aptarnavus klientą prie kasos, jo vežimėliu iš karto gali naudotis naujas klientas).

  4. Programos parametrų failas 500 modeliavimo laikas 5 kasu skaičius 50 kliento atėjimo tikimybė (%) 40 maksimalus kliento apsipirkimo laikas 10 maksimalus kliento aptarnavimo prie kasos laikas

  5. Eilėje saugomų duomenų tipas unit QueueData; interface type QueueDataType = ...; implementation end.

  6. ADT Eilė unit Queue; interface uses QueueData; type QueueType = ...; procedure createQueue (var queue : QueueType); function isEmptyQueue (const queue : QueueType) : boolean; function isFullQueue (const queue : QueueType) : boolean; procedure enQueue (var queue : QueueType; data : QueueDataType; var err : boolean); procedure deQueue (var queue : QueueType; var data : QueueDataType; var err : boolean); procedure firstInQueue (const queue : QueueType; var data : QueueDataType; var err : boolean); function lengthOfQueue(const queue : QueueType) : integer; procedure destroyQueue (var queue : QueueType); implementation

  7. Programa program Shop; uses QueueData, Queue; const PARAMS_FILE_NAME = 'params.txt'; MAX_CASH_DESKS = 10; MAX_ACTIVE_CLIENTS = 20; { Global variables } var errors : boolean; simulationTime,noOfCashDesks,newClientProbability, maxBuyingTime, maxCashingTime : integer; procedure loadParams; ... { Program variables } var time,maxNoOfShoppingCarts,usedShoppingCarts,noOfActiveClients, i, j, k : integer; cashingTime : QueueDataType; activeClients : array[1..MAX_ACTIVE_CLIENTS] of integer; cashDesks : array[1..MAX_CASH_DESKS] of QueueType; cashingLeft : array[1..MAX_CASH_DESKS] of integer; begin loadParams;if errors then exit; ...

  8. Programa (2) while not errors and (time < simulationTime) do{ Main simulation loop } begin inc(time); { Get new client } if random(100) <= newClientProbability then begin { New client should be added to active clients } inc(noOfActiveClients); if noOfActiveClients > MAX_ACTIVE_CLIENTS then begin writeln('Number of active clients become too big ( >', MAX_ACTIVE_CLIENTS, ' ).'); errors := true; break; end; activeClients[noOfActiveClients] := time + random(maxBuyingTime) + 1; { New client gets a shopping cart } inc(usedShoppingCarts); if usedShoppingCarts > maxNoOfShoppingCarts then maxNoOfShoppingCarts := usedShoppingCarts; end; { Check active clients who finished buying } ... { Check queues at cash desks } ... end; { Main simulation loop }

  9. Programa (3) { Check active clients who finished buying } j := 0; for i := 1 to noOfActiveClients do begin if activeClients[i] > time then begin inc(j); activeClients[j] := activeClients[i]; end else begin k := random(noOfCashDesks) + 1; cashingTime := random(maxCashingTime) + 1; enQueue(cashDesks[k], cashingTime, errors); if errors then begin writeln('The queue of cash desk becomes too long.'); break; end; if lengthOfQueue(cashDesks[k]) = 1 then cashingLeft[k] := cashingTime + 1; dec(noOfActiveClients); end end;

  10. Programa (4) { Check queues at cash desks } for k := 1 to noOfCashDesks do if lengthOfQueue(cashDesks[k]) > 0 then begin dec(cashingLeft[k]); if cashingLeft[k] = 0 then begin deQueue(cashDesks[k], cashingTime, errors); if errors then begin writeln('Program error: trying to dequeue.'); break; end; if lengthOfQueue(cashDesks[k]) > 0 then begin firstInQueue(cashDesks[k], cashingTime, errors); cashingLeft[k] := cashingTime; end; end; end;

  11. Programa (5) { Output simulation results } writeln('Max number of shopping carts is ', maxNoOfShoppingCarts); { Clearing data structues } for i := 1 to MAX_CASH_DESKS do destroyQueue(cashDesks[i]); end. Pilnas programos tekstas bus pateiktas internete.

  12. Programos vykdymas D:\MIF\A&DS\_Pvz>shop_a Max number of shopping carts is 244 D:\MIF\A&DS\_Pvz>shop_a Max number of shopping carts is 244 D:\MIF\A&DS\_Pvz>shop_a Max number of shopping carts is 244 Pagrindinės programos pradžioje pridėjus: Randomize; D:\MIF\A&DS\_Pvz>shop_r Max number of shopping carts is 257 D:\MIF\A&DS\_Pvz>shop_r Max number of shopping carts is 256 D:\MIF\A&DS\_Pvz>shop_r Max number of shopping carts is 267 D:\MIF\A&DS\_Pvz>shop_r Max number of shopping carts is 251Ar programos rezultatai teisingi?

  13. Apibendrinimas Visada vertėtų pavertinti, ar programos rezultatai prasmingi. Modeliavome 500 laiko vienetų, o kliento atėjimo tikimybė yra 50%. Taigi per visą laiką turėtų ateiti apie 250 klientų. O programa sako, kad tiek vežimėlių ir reikia. Kyla įtarimas, kad vežimėliai neatlaisvinami... Patikrinus, pasirodo, kad programoje praleistas dec(usedShoppingCarts);

  14. Klausimai ?

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