Elevators

Don't forget the executive elevator algorithm (EEA), which uses a priority interrupt to take passengers directly to the top floor.

Over the years, I've witnessed numerous instances of poor elevator behavior:

- Two elevators ascending and descending in near lock step, in a two-elevator building, effectively reduced to one elevator.

- When going in a different direction from the requested one (e.g. called elevator to go up, but actually going down), the doors wastefully close, open and close again. Seen this in many elevators.

- At 3 a.m. you take the elevator to a parkade, like to get something from a car. When you return to the elevator a minute later, it is gone; it spontaneously moved away even though nobody is using it but you.

If you like elevator hacking don’t forget the seminal DEF CON talk by Deviant Ollam and Howard Payne: https://youtu.be/oHf1vD5_b5I

I watch it like once a year because it always tickles some part of me. Like all the different modes you can get an elevator into. The most fancy one people might encounter is when moving into or out of a building. The front office can give you a key to give exclusive control over an elevator so your movers aren’t waiting around on elevators. Put it in that mode and it will stop responding to calls from other floors. Only the person with the key can control the elevator. You get on, select the floor, door closes elevator goes, and then just chills there with the door open waiting for you. Annoying for the rest if the building (the building is down an elevator when in that mode) but is amazing for the person using it! But there are way, way more depending on the installation and function.

Fun fact: most elevator shafts are sealed at the top as tight as possible to prevent them from becoming a giant chimney in a fire. It never even occurred to me until I was in a mechanical room wondering “where is the hatch to look down the shaft?” The answer is “there is none, and it’s a feature not a bug.” You want to block all airflow so fire doesn’t chase up the shaft into neighboring floors. Who knew!

Lol, love this post. Every single day when I take the elevators at the office I try and figure out what the algorithm is behind it. Been too lazy to just research it. Now I know!

This article gives me war flashbacks about a particularly irritating OO design interview from 5 years ago.

This is super interesting. I've always wondered how the complicated things work!

I didn't realize that neal.fun had some competition.

I've always wondered about elevator algorithms. This is awesome.

As someone who lives in a penthouse, elevator’s frustrations are real struggle especially in rush hours, because the elevator has to travel dedicated to you rather than you piggy backing on one that is already going up or down.

I love elevator simulations.

Having gone to many large furry cons(notoriously brutal on the elevators due to how much floor-to-floor traffic there is compared to other usage) I’ve seen these algos basically completely fail to adapt to unusual patterns. I once spent over half an hour on checkout day, in a hotel with 8 banks, to even have a car stop on our floor at all. Can’t really blame the algo for such a unique situation and at the end of the day a saturated system is a saturated system and nothing can be done to make it fast, but it’s always interesting to witness when a system is completely unable to accommodate a demand like that.

(In the example above we gave up and decided it was cardio time, five laps up and down 14 flights to escape with all our luggage.)

Maybe I missed it, but the algorithm should also redistribute empty elevators that stop too closely to each other.

>All this technology just to underperform the S&P

My takeaway is that the benefit of using a much more complex algorithm is marginal.

This is a good article. It reminds me of a story.

At a previous employer we had heteregenous elevators. In one bank, some went to the lower half of floors only while others went to all and the company installed a "smart" elevator system. I kind of became known because I was constantly yelling about this system in the feedback group because I hate "smart" elevators and and (IMHO) they just don't work. What actually works is express elevators and sky lobbies.

This article covers one of the deficiencies this system had: full elevators. For example, you'd want to go down and an elevator would skip your floor because another had already been assigned. That one would show up full and you couldn't go down. Down wasn't so bad because the stairs weren't a bad option but up was terrible. Going up a few floors was fine. Going up 20 was... a bigger issue.

Back in the day we had elevator operators and people in the lobby during the morning rush who would shepherd people into particular elevators. I actually think this system works way better than anything technology has come up with. Even if you nail the implementation (and I've never experienced elevators that have), people don't read and will just get into elevators anyway.

Anyway the article says that generally speaking on smaller banks simple up and down buttons work best. I absolutely agree.

There's a deeper issue here though and that is solutions looking for a problem. Nobody is making money from up and down buttons. They are fromn selling smart elevator solutions. And you see this everywhere in life. It basically devolves into rent-seeking behavior. Salespeople wine and dine a couple of people responsible for making decisions and then make bank on selling something nobody wants or needs as well as the constant maintenance and updates.

> Everyone has shared the frustration of waiting for an elevator that never seems to arrive.

Really? Maybe I'm lucky I never had to deal a lot with elevators.

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did he factor in the lifting speed?

Enjoyed the read, thanks!

Beyond the content, the font, style, etc made it a pleasant experience for me.

I think this comparison is also assuming the distribution of request & requested floor is uniform? When actually near pairs are less likely (I'll just take the stairs) than bottom to top, so even analysing it is more complex than at first glance.