2026

Formal perturbation theory, and in particular singular perturbation theory, are standard topics in applied mathematics, but seem to be largely unknown outside that specific community. Which is a shame, because they are both useful, and intellectually fascinating.

Perturbation expansions, in particular for higher orders, have a reputation for being “cumbersome”, as the say: the algebra quickly becomes both tedious and error-prone. Which is true, but it turns out that the SymPy computer-algebra system can be put to good use in this context.

It turns out, Caltech has made the Feynman Lectures available online on their website.

Occasionally, I like to drink hot chocolate — that is, real hot chocolate, from pure cocoa powder and whole milk; not some (sugared, flavored) drink mix.

So, I was somewhat devastated when I learned that the venerable, time-honored Droste (those of the Droste Effect) seems to have gone tragically out of business.

Some replacement was required: at least as good as the original, and satisfying my various purist predilections.