Relearning differential equations, laplace/fourier/transforms in general, orthogonal polynomials, special functions, integral equations, greens functions etc. Also learning distributed systems, systems, networks, graph theory, software design patterns, and am planning on relearning multivariable calculus and tensor calculus. eventually plan to go back and reteach myself physics in a more mathy way.
I'm a math/phys double major who got a job in software.
