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Where to wait for an elevator (2010)

johndcook.com

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Re: Where to wait for an elevator (2010)

#41

Post by Jtsummers »

kazinator wrote: post #30

> So standing in front of the second elevator minimizes the expected distance to the next elevator, assuming all three elevators are equally likely to arrive next. > What if you want to minimize the worst case instead of the average case? Stand half way between the first and third elevators. What is the difference between "in front of second" and "halfway between first and third"?

From the problem statement (first two sentences of the post):

> Imagine a bank of three elevators along a wall. The elevators are in a straight line but they are not evenly spaced.

Re: Where to wait for an elevator (2010)

#42

Post by troglonoid »

kazinator wrote: post #30

> So standing in front of the second elevator minimizes the expected distance to the next elevator, assuming all three elevators are equally likely to arrive next. > What if you want to minimize the worst case instead of the average case? Stand half way between the first and third elevators. What is the difference between "in front of second" and "halfway between first and third"?

In the first paragraph he says the elevators aren’t evenly spaced, and then again, it is mentioned in the James Hadley quote.

In this scenario, the second elevator isn’t centered between the first and the third elevators.

If I understand the description properly, the layout may be something like this:

[]__[]____[]

Re: Where to wait for an elevator (2010)

#44

Post by ThePadawan »

ehvatum wrote: post #26
ThePadawan wrote: post #7

Earlier quoted context omitted.

I live in a building that has this. As a resident - it works. Whoever made this building made a whole lot of mistakes though: - They put this into a building with public spaces (e.g. a doctor's office). - When standing in front of the elevators, nowhere does it say which office is on which floor (it says so in the lobby which you walked by to get to the elevators) - The screens where riders have to select floors auto…

I wonder if there is any improving that system without replacing it.

There are some easy fixes to the things I described - like adding a list of offices and floor numbers above the touchpads, or adding a phone signal boosting indoors antenna.

Apart from that, the first thing I wondered when I moved in was "oh, as a resident, does that mean I just get a keyfob I can wave at this screen that knows I live on the X-th floor?". That's also feasible, to the degree that the Wikipedia article linked above refers to this.

The problem with all these fixes is of course that they all cost more than $0.

And neither the company owning this building nor any landlord company involved in its operation is even based in the same ZIP code as the building. So why would they care?

Re: Where to wait for an elevator (2010)

#45

Post by deathanatos »

layer8 wrote: post #27
baxtr wrote: post #8

Might be a bit off-topic… But: The one big question I have with elevator UX is this: why isn’t it possible to deselect a choice? So pressed 10th floor but wanted 11th. There is no way to press button 10 and then button 11 to correct that mistake. Will I ever solve this mystery?

There are two cases where deselecting a floor would complicate the logic: 1. When the currently targeted floor is deselected and the remaining selected floors are all in the other direction: Then the elevator would have to either reverse course without stopping — a situation which otherwise doesn’t occur and would be unexpected and possibly dangerous for the passengers — or stop on a non-selected floor before changin…

I didn't think elevators permitted scenario 1 to occur at all; I thought they refused to allow selecting floors not in the direction of travel.

(I don't usually board elevators traveling in the wrong direction, ofc., so, I'm not that sure.)

Re: Where to wait for an elevator (2010)

#47

Post by halfnormalform »

eddd-ddde wrote: post #17
mulmen wrote: post #11

Earlier quoted context omitted.

Because you could deselect other peoples choices.

This isn't an argument, as you can also select other people's non-choices.

Elevators sometimes have an anti-mischief feature where they will deselect every floor if all the floors are selected in a brief period of time. The cab will slow to a stop if no new buttons are pressed. It’s kind of eerie, actually.

Re: Where to wait for an elevator (2010)

#48

Post by zerocrates »

deathanatos wrote: post #45
layer8 wrote: post #27

Earlier quoted context omitted.

There are two cases where deselecting a floor would complicate the logic: 1. When the currently targeted floor is deselected and the remaining selected floors are all in the other direction: Then the elevator would have to either reverse course without stopping — a situation which otherwise doesn’t occur and would be unexpected and possibly dangerous for the passengers — or stop on a non-selected floor before changin…

I didn't think elevators permitted scenario 1 to occur at all; I thought they refused to allow selecting floors not in the direction of travel. (I don't usually board elevators traveling in the wrong direction, ofc., so, I'm not that sure.)

I haven't done it in a while but my recollection is that if you press a "wrong-direction" floor it will just go there after having completed all the previously-selected stops.

Re: Where to wait for an elevator (2010)

#49

Post by OisinMoran »

"Since you can’t move without increasing the average distance, you must have started at the best spot."

Technically this isn't a fully sound inference. All this proves is that you're at a local optimum. So you'd also need to know or show that there is only one optimum/the problem is convex/local=global or any variant.

Of course that is the case here, but it's always worth noting the specific properties of a problem that make a neat solution possible.

Re: Where to wait for an elevator (2010)

#50

Post by butterNaN »

baxtr wrote: post #8

Might be a bit off-topic… But: The one big question I have with elevator UX is this: why isn’t it possible to deselect a choice? So pressed 10th floor but wanted 11th. There is no way to press button 10 and then button 11 to correct that mistake. Will I ever solve this mystery?

I have been to a few elevators in India where you can deselect a choice like you described. However they are not rare.
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