Quadratic optimization of fixed points for a family of nonexpansive mappings in Hilbert space.
Let X be a Banach space over ℂ. The bounded linear operator T on X is called quasi-constricted if the subspace is closed and has finite codimension. We show that a power bounded linear operator T ∈ L(X) is quasi-constricted iff it has an attractor A with Hausdorff measure of noncompactness for some equivalent norm ||·||₁ on X. Moreover, we characterize the essential spectral radius of an arbitrary bounded operator T by quasi-constrictedness of scalar multiples of T. Finally, we prove that every...