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Terrence Chan

follow me as I play poker and look for new ways to get punched in the face

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elevator wait time function?
From something a little meatheady to something a little nerdy now. (What else would you expect from me?) I recently bought a new apartment in Vancouver. My old apartment had three elevators, but in this one they cheaped out and only bought two. Both buildings have a similar number of units (about 200). It's very clear to me that the increase in wait time going from 3 to 2 is more than 50%, but I'm not sure what the difference actually is.

For the last 48 hours, we've been operating with just one elevator and it's just been a painful experience. Yesterday, the process of taking out the garbage and coming back up to my apartment took 17 minutes. Maybe wait time exponentially increases with elevators going out of service?

In something that is not as easily calculated, people also change their behaviour. You can take the stairs down in our building (fire exit) but not up (you can't gain access to the living floors). So presumably some people are taking the stairs down. Also, I talked to a woman yesterday who goes to work at 8am and as part of her morning plan, actually goes out and presses the elevator call button, then goes back into her apartment to make breakfast and eat it. Behaviour like this must necessarily increase wait time since some non-zero percentage of the time, the elevator comes right away and she isn't there.

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I often find myself analyzing the utter inefficiency and stupidity of most elevator algorithms. I did this a lot in Las Vegas, waiting for a (non-full) elevator; where they obviously have the money to install a decent system, but just haven't bothered to.

The best systems have as simple console asking you what floor you want, and then telling you which elevator to take. However a lot of improvements to the algorithm can still be made using only the binary up/down decision by the user; even in the extreme case of one elevator.

can still be made using only the binary up/down decision by the user;
And then the people come and push both up and down buttons.

If the requests for the elevator become frequent and chaotic enough, it is actually better to just let it go from top to bottom floor and back, with necessary stops in between.

Except you get a situation where the elevator is full but continues to stop on every floor for no purpose. This gets really annoying on very tall buildings that don't segregate elevators to certain floors. Obviously you want to pay attention to the weight sensor to detect a nearly full elevator and stop making pick-up-only stops. If you open for a few pick-up-only stops and the weight doesn't change, you also have a good idea to stop doing that and continue to the 1st drop-off ordered floor.

I don't think Terrence's question can be answered simply, because there are many different ways to program elevators, some better than others.

Learn something new every day.

In areas with large populations of observant Jews or in facilities catering to Jews, one may find a "Sabbath elevator". In this mode, an elevator will stop automatically at every floor, allowing people to step on and off without having to press any buttons. This prevents violation of the Sabbath prohibition against operating electrical devices when Sabbath is in effect for those who observe this ritual.


This is supposedly also true for certain intersections near synagogues in Los Angeles, where the lights are on an automatic cycle to avoid having pedestrians set off traffic sensors.

(according to http://www.amazon.com/Traffic-Drive-What-Says-About/dp/0307264785)

Traffic is a classic programming discussion that has a recursive nature. It is a typical classroom problem that lends itself to advanced discussion. And, it is extensively used in the real world.

yeah, elevators suck

I live in a fairly similiar-sized building in Toronto: 200 units, two elevators. I avoid them like the plague in any sort of busy time, especially the morning. Waste of time. Just take the stairs. (You're trying to be super-fitness guy anyways, aren't you? ;-)

Of course I live on the 6th floor, and as far I'm concerned anyone who doesn't use the stairs most of the time to get to our floor.. well.. no comment. (*cough* LAZY *cough*) From the parking garage it's difficult if not impossible, unfortunately.

And yeah when one of them is in service, don't even bother.

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