mystran wrote:andy-cytomic wrote:mystran wrote:Well, in the thread you mentioned (at least not in the original post), I don't remember doing any nodal analysis, because I just pretty much assumed a bunch of differential equations as the ground truth.
Ok so where did the differential equations come from?
You're missing the point. Getting from a circuit to code is really a two step problem: first you need a model of the circuit, and then you need a method for numerically solving the model. You can solve each of these sub-problems separately and they are essentially independent as far as particular techniques go.
I (quite explicitly I might add) made no attempt to do anything about the first part in that thread (because the thread wasn't about circuit modeling; it was about zero delay filters), so there was no need to even consider MNA. I picked a bunch of familiar equations as given, and it doesn't really matter how those equations came to be, since the subject was the second part: how to write an implementation that numerically solves those.
I'm making such a fuzz about this, because I think both problems are interesting on their own right... but at the same time you can pretty much "plug and play" any solution for any of the sub-problems and still have it all work just fine.
No points were missed, I was letting people know the first step exists and needs to be solved at some point, and not glossing over that fact.
Yes, the two problems can be separated if you want, but they don't have to be, please point out where I have said otherwise and I will correct what I have said.
Writing down the possibly non-linear differential equations has nothing to do about "feedback" as such, for many circuits you can write down such equations and there is no feedback at all in the original circuit that needs solving without adding a delay. For example the passive RC and active one pole low pass filters have identical differential equations, but one original circuit had feedback and one didn't. There is no "feedback" as such in the resultant equation (they are both the same) since they abstract out such things and just represent the system as possibly implicit equations to solve.