I am using the WKB method to find approximate soltuions to 2nd order linear ODE's,
such as the one found in the example on wikepedia here: https://en.wikipedia.org/wiki/WKB_approximation
Or the nth order Bessel function.
I want to find a general expression for the error, or perhaps even one for specific ODE's, and the ones I've found on similar sources come with no explanation as to how its derived or how to find such an expression for a more general case. If someone could please explain how the approximation for nmax and the subsequent approximation for the term of that order is found, it would help greatly.
Apologies if my question is bad, but I genuinely cannot find any answers for something like this from any source.