Unstructured Perturbation

qProblem: Given *M *Î **C*** **p**´** q* , find a smallest *D* Î **C*** **p**´** q* (no structure imposed on *D*) in the sense of
such that det(*I-M**D*)*=0.*

It
is easy to see that

with
a smallest “destabilizing”

So
**the
largest singular value of ***M* can be defined as