AN EXTENSION OF THE VARIATIONAL INEQUALITY APPROACH FOR OBTAINING CONVERGENCE RATES IN REGULARIZATION OF NONLINEAR ILL-POSED PROBLEMS

Convergence rates results for Tikhonov regularization of nonlinear ill-posed operator equations in abstract function spaces require the handling of both smoothness conditions imposed on the solution and structural conditions expressing the character of nonlinearity. Recently, the distinguished role of variational inequalities holding on some level sets was outlined for obtaining convergence rates results. When lower rates are expected such inequalities combine the smoothness properties of solutions and forward operators in a sophisticated manner. In this paper, using a Banach space setting we are going to extend the variational inequality approach from Holder rates to more general rates including the cade of logarithmic convergence rates.