Robust stability of multivariable systems with both real parametric and norm bounded uncertainties

The robust stability of a multivariable system with both structured real parametric and unstructured norm bounded uncertainties is considered. It is shown that if the real parametric uncertainty enters only linearly and independently into the numerator matrix and the denominator characteristic polynomial, then the robust stability (or stability margin) can be tested (or calculated) exactly. It is also shown that this in fact gives a way to compute a class of real structured singular values