Thursday, September 20, 2007

Elevator Algorithms and Progressive Parking

My parents' Manhattan apartment is on the ninth floor. To get there, you have to take an elevator and then thread your way through a labyrinthine hallway painted in several hideous shades of green. The hallway carpet is an Escherian print in gray-greens. The hallway floor is uneven, and the walls and ceiling are not quite square.

The combination of colors, floor waves, and tilted frame in the hallway never failed to make me seasick.

Perhaps this is why I paid so much attention to the movement of the elevators. The elevators displayed their current locations and direction of travel. Over the week, I was able to observe their operation many times.

Many years ago, we modeled the efficient movement of elevators in a computer class. Elevator algorithms are used for many problems in computer science (like the efficient movement of disk drive arms), and the ones used in actual elevators are often quite stupid.

The elevator algorithm in my parents' apartment building, however, was one of the smartest I've ever seen. It almost always sent the closest elevator to pick us up and it never, ever sent two elevators.

I salute those elevators.

In my parents' neighborhood, there's no parking for private automobiles. Commercial vehicles can park by purchasing time from machines along the street. The parking rates are $2 for one hour, $5 for two hours, and $9 for three hours.

I had never heard of progressive parking rates before, but it makes perfect sense in Manhattan.

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