Shortcut and Delay
Shortcut for previous working directory. Equations with a small delay.
I mentioned a bash shell feature in the previous newsletter. I’ve got another one for this newsletter: ~- (tilde dash) for referring to the directory you were in before moving to your current directory.
This feature has been around for decades, but I just learned about it. And I used it a few times already.
A delay-differential equation specifies a relationship between a function, its derivatives, and its values at earlier times. If the delay is small enough, then the solution to the equation with a delay behaves similarly to the solution to the equation without a delay. This post makes that statement precise for a simple case and shows a couple examples.
Delay terms can make a model more realistic. They also can make the solutions more interesting.
