This video introduces the concept of "singular perturbation theory" applied to ordinary differential equations, in setting a small parameter to zero changes the character (e.g. order) of the differential equation. The resulting series is then an asymptotic series. We discuss solvable examples where the behavior of the solution can be obtained easily, setting up our discussion of boundary layer and WKB theory. Video created for PHYS 201 at UCSD in Fall 2019.
