This isn't exactly a math question (apologies!), but it could prevent many potential misunderstandings I might otherwise encounter in the near future (and also prevent many dumb questions I will post here otherwise). What is a common reference for linear, time-varying systems?
I saw two references: Linear System Theory by Wilson Rugh, and Control of Linear Parameter Varying Systems with Applications by Mohammadpour and Scherer.
Background
Recurrent neural networks (RNNs) and structured state-space models (SSMs) have been suffering from the vanishing/exploding gradient problem. Recent progress in sequence modeling suggests that these problems stem from time-invariance. I am wondering where I should start to catch up on the general knowledge of time-variant systems.