Monday, November 11, 2019

transfer function - Does instability make an otherwise LTI system nonlinear (or time-variant)?


I am spinning this question off from the question from johnny. Matt L. and I have had directly opposite conclusions to johnny's question.


I want to decouple the question from issues of causality and other goofy stuff.


So we have a simple first-order recursive system described with time-domain I/O equation:


y[n]=py[n1] + x[n]nZ


Of course, the Z-transform of this is


Y(z)=pz1Y(z) + X(z)


and transfer function



H(z)


We would normally identify this as a simple and realizable LTI system with a zero at 0 and a pole at p. But in the other question, there is an issue regarding linearity and time-invariance for the case when p=-1 \ .


For what values p is this system linear? For what values p is this system time-invariant?


This is, I believe, the kernel of the disagreement I have with Dr. Matt L.




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