A converse result for Banach space convergence rates in Tikhonov-type convex regularization of ill-posed linear equations
Provides theoretical optimality guarantees for regularization in Banach spaces, relevant for inverse problems researchers.
The paper proves that variational source conditions yield optimal convergence rates for Tikhonov regularization in Banach spaces, extending Hilbert space converse results without spectral theory.
We consider Tikhonov-type variational regularization of ill-posed linear operator equations in Banach spaces with general convex penalty functionals. Upper bounds for certain error measures expressing the distance between exact and regularized solutions, especially for Bregman distances, can be obtained from variational source conditions. We prove that such bounds are optimal in case of twisted Bregman distances, that is, the rate function is also an asymptotic lower bound for the error measure. This result extends existing converse results from Hilbert space settings to Banach spaces without adhering to spectral theory.