I'm not sure if I understand the following correctly, but it seems to have appeared implicitly in my studies.
If Zcl, Zp, and Zℏ are the classical, perturbative to arbitrary order, and full nonperturbative solutions to the generating function of some quantum field theory, then the three functions arise as (approximate) solutions to a Schrödinger-like equation of the form
y′(x)=f(x)⋆y(x)
for some definition of the star product. To my knowledge Zp is reproduced (derived?) by the solution to the above ODE with Picard's method, and moreover if one takes the limit ℏ→0 either beforehand or in the perturbative solution, one obtains Zcl. However if one solves it first then takes the limit, there is some ambiguity with convention and the classical solution is not obtained:
limℏ→0Zℏ≠Zcl=limℏ→0Zp
I've heard the first equation as an explanation for why the perturbation series is riddled with divergences (i.e. the generating function has a discontinuity at ℏ=0, among other reasons), but haven't seen something substantive on the topic.
How does one recover the classical solution and perturbative series given Zℏ? A Taylor series doesn't seem to work because of the discontinuity.