>Of course! This is stuff I did when I was in high school years ago ! In college, I learned about active synthesis which is creating equivalent LC circuits out of OpAmps and RC elements -- using a potentiometer to modulate frequencies.

I meant variable capacitors in their actual meaning and not analogs, so I guess I wouldn't have even
call a varicap a variable capacitor, but well it seems this is now the convention. Yes I think one can use a potentiometer to modulate frequencies with OpAms and RC elements (my husband does actually some circuits like these) and even alternating voltage sources but whatsoever even if you do frequency modulation and triggering in an LC circuit analog setting I am not sure wether the Mathieu equation models a generic behaviour of such a circuit (in particular if you look at the derivation of the LC circuit equation I see problems) and at a first glance I would think that the Mathieu equation would anyways not model the behaviour I was describing, but I would need to look at this longer and I don't have the time for that.