Concerning the problem of calculating the transfer function of a third-order filter; see Help deriving the transfer function of an LC circuit?
A method kindly explained by Verbal Kint is 'FACTs', which takes the grind out of the process. This method requires the derivation of time constants, and includes nulling the input, setting a reactive component to either a DC or a high frequency state and finding the resistances driving the other components.
The time constants that were included are:
tau1, tau2, tau3,tau12, tau13, tau23, tau32,tau123
My question is, would there not be more time constants to include, for example, tau132, tau 231, etc.? I'm unsure why an exhaustive set isn't included.
I'm pretty new to this subject, so any input would be appreciated.