simulation

Why simulation?

provide predictable and quantifiable results for "what if" scenarios

What's needed for simulation?

• identify what kind of data we want to get

• understand the variables that we want to change

  • derive an "operational model" for writing simulation program

A typical customer checkout scenario

customers with items wait in a queue

servers services customer

Typical questions for managers (i.e. simulation conclusion)

Given a customer pattern (arrival time, # of items),

• • • what is the waiting time, average, max, etc?

    • what is server efficiency? (how busy is the server?)

    • how many servers do we need to keep customers happy?

Data structure

Main Simulation Routine

// set up data structure

queue<customerType> customerQueue;

serverListType serverList(numberOfServers);

// loop the whole simulation

for (clock = 1; clock <= simulationTime; clock++) {

// update transaction time in server (if busy)

// update waiting time in customer

QserverList.updateServers(cout);

if (!customerQueue.empty()) updateCustQueue(customerQueue);

// see if any new customer arrives during this clock period

// if it does, queue it up

if (isCustomerArrived(timeBetweenCustomerArrival))

{

custNumber++;

customer.setCustomerInfo(custNumber,clock,0, transactionTime);

customerQueue.push(customer);

}

// see if any server is free

// if there is, assign a customer

serverID = serverList.getFreeServerID();

if (serverID != -1 && !customerQueue.empty())

{

customer = customerQueue.front();

customerQueue.pop();

serverList.setServerBusy(serverID, customer);

}

}

Discussions

• What if we have multiple customer queue? Quick checkout in supermarket, or first class in airline?

• How about reading customers arrival record from file? This is, in my opinion, the most flexible way of doing simulation. It provides "repeatability" which is important in collecting consistent data.

• So, what if we still want to do mathematically generated customer pattern? Well, we can generate it mathematically and write it to a file....