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October 2025 M T W T F S S 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Category Archives: Simulation
A Simple Discrete-Event Simulation: Part 14
Today I modified the entry component so it creates new entities according to a supplied schedule. This can be made as complex as we’d like but let’s keep it simple for now: the input parameters are the duration of each … Continue reading
A Simple Discrete-Event Simulation: Part 13
Today I wanted to streamline the code in the activate method for the entities that apply the advance command. I started by breaking the code in the series of if statements out into separate methods, which at least makes things … Continue reading
A Simple Discrete-Event Simulation: Part 12
Today I wanted to start constructing an Entry component. I created a very simple on that generates modeled entities are regular, defined intervals over the duration of the simulation run. Here’s the relevant code.
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//time to end the entire simulation var endSimTime = 1440.0; //time increments in minutes, run for 24 hours //collection of all entities in the system var setOfEntities = new Array(); //Entry component function entryComponent(arrivalsPerHour) { //initially assume it just generates entity1s that disappear after a single cycle this.entityID = getNewID(); this.initialTime = 0.0; this.incrementTime = 60.0 / arrivalsPerHour; this.endTime = endSimTime; this.nextState = "increment"; feq.newItem(globalSimClock,this); //assume all components created at time zero this.generateNewEntity = function() { var newEntity = new entity1(globalSimClock,2.0,globalSimClock+1.0); setOfEntities.push(newEntity); } this.activate = function() { if (this.nextState == "increment") { this.generateNewEntity(); //<<<< this one line does all the meaningful work <<<< displayProgressText("Entry component "+this.entityID+" generates new entity at time "+globalSimClock+"<br />"); if (globalSimClock + this.incrementTime >= this.endTime) { this.nextState = "destroy"; } advance(this.incrementTime); } else if (this.nextState == "destroy") { displayProgressText("Entry component "+this.entityID+" terminated at time "+globalSimClock+"<br />"); } else { alert("Entry component "+this.entityID+" went into undefined state"); displayProgressText("entity "+this.entityID+" in undefined state at time "+globalSimClock+"<br />"); } } }; //entryComponent var entry1 = new entryComponent(2.0); |
This generates the following output. … Continue reading
A Simple Discrete-Event Simulation: Part 11
Now that we have a couple of basic mechanisms in place for building discrete-event simulations let’s apply them to some actual components we can use to represent something real. A very simple system might consist of the following four components … Continue reading
A Simple Discrete-Event Simulation: Part 10
Today I defined some new entities that better illustrate the operation of the wait mechanism and the current events queue, which I have modified so it scans the list of current items repeatedly until no conditions are met. Here’s the … Continue reading
A Simple Discrete-Event Simulation: Part 9
It’s one thing when you place an entity back in the future events queue at a specific absolute or relative time, but it’s quite another if you want an entity to become active when a certain condition–or set of conditions–becomes … Continue reading
A Simple Discrete-Event Simulation: Part 8
Today I automated the generation of entity IDs. First we create a basic counter.
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var globalIDCounter = 0; function getNewID() { return ++globalIDCounter; } |
Then we change the entity declarations to remove the explicit assignment of IDs as we have been doing.
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function entity1(initialTime,incrementTime,endTime) { this.entityID = getNewID(); |
That was pretty mindless, so let’s … Continue reading
A Simple Discrete-Event Simulation: Part 7
Today we’ll do some more streamlining. We’ll start by adding a new function to the futureEventsQueue object.
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this.newItem = function(time,entity) { //create futureEventItem var feqItem = new futureEventItem(time,"absolute",entity); this.insertTime = feqItem.getActivationTime(); globalInsertTime = this.insertTime; if (this.feqSize == 0) { this.feq[0] = feqItem; this.feqSize++; console.log("Array size: "+this.feq.length); } else { //find index of feq item to insert before var insertIndex = this.feq.findIndex(this.findLaterTime); //insert the element if (insertIndex < 0) { insertIndex = this.feq.length; } this.feq.splice(insertIndex,0,feqItem); this.feqSize++; console.log("Array size: "+this.feq.length); } }; |
Then, instead of having to specify the “absolute” (vs. “advance”) flag in the initialization of a new entity object, we know we’ll … Continue reading
A Simple Discrete-Event Simulation: Part 6
Now that I’m sure the basics are working the way I’d like I want to see if I can streamline things some more. The first thing to do is recognize that the next item being pulled off the future events … Continue reading
A Simple Discrete-Event Simulation: Part 5
Adding a second entity works correctly.
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var entityA = new entity(1,11.0,10.0,100.0); var entityB = new entity(2,13.0,13.0,100.0); |
104 minutes entity 1 created at time 0 entity 2 created at time 0 entity 1 updated at time 11 entity 2 updated at time 13 entity 1 updated at time 21 entity … Continue reading