Abstract:
It is shown that the joint spectral radius $\rho(M)$ of a precompact set $M$ of operators on a Banach space equals the maximum of two numbers, the joint spectral radius $\rho_{e}(M)$ of the image of $M$ in the Calkin algebra and the BW-radius $r(M)$. Similar results related to general normed algebras are also obtained. The proofs are based on the theory of topological radicals of normed algebras.
Keywords:joint spectral radius, the Berger–Wang formula, topological radical, invariant subspace.