Consider a pair of LC oscillators, one with capacitance C1 and inductance L1 and the other with capacitance C2 and inductance L2. Suppose they're connected through a capacitor Cg. We want to find the normal modes and frequencies.
If we write out Kirchhoff's laws, we find V1+¨V1(1+ϵ1)/ω21−(ϵ1/ω21)¨V2=0V2+¨V2(1+ϵ2)/ω22−(ϵ2/ω22)¨V1=0 where ϵi≡Cg/Ci and ω2i≡1/LiCi. These equations can be written in matrix form as (V1V2)=((1+ϵ1)/ω21−ϵ1/ω21−ϵ2/ω22(1+ϵ2)/ω22)(¨V1¨V2). Now if L1=L2 and C1=C2 then ϵ1=ϵ2≡ϵ and ω1=ω2≡ω0 and the matrix equation becomes (V1V2)=((1+ϵ)/ω20−ϵ/ω20−ϵ/ω20(1+ϵ)/ω20)(¨V1¨V2). In this particular case, the matrix can be written in the nice form 1+ϵω20I−ϵω20σx and it's pretty easy to find the normal modes and normal frequencies.[a]
However, when the oscillators aren't identical, e.g. Eq. (⋆), expressions for the normal modes and frequencies are pretty messy. Is there a transformation we can apply to (⋆) to bring it into a simple form like (⋆⋆) so that the mode analysis results in simpler equations?
Perhaps another way to ask this would be to ask for a systematic way to rescale the variables so that the matrix in the equations of motion is symmetric or perhaps Hermitian.
[a] The frequencies are ω0 (even mode) and ω0/√1+2ϵ (odd mode).
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