As of this moment, I’m working my way through “Mathematical Methods in the Physical Sciences” by Mary Boas, which I recommend. However, my TT “event” caused me to forget many of the ideas and skills I’d acquired in public school and college, and this is onerous and is becoming intolerable. So I’ll be taking the inefficient approach of fighting on two fronts: acquiring new subjects and relearning the old ones.
On the first front, I intend to move from applied methods of calculus to real analysis, complex analysis, and modern algebra. I believe algebra will be the more amenable to my tastes and talents.
On the second front, I’ve drawn a starting line at the undergraduate level. I intend to work back through linear algebra, calculus (differential, integral, multivariate), differential equations, partial differential equations, calculus-based probability and statistics, and introductory proof techniques and symbolic logic.