Böttcher, Albrecht ; Hofmann, Bernd ; Tautenhahn, Ulrich ; Yamamoto, Masahiro : Convergence rates for Tikhonov regularization from different kinds of smoothness conditions
Böttcher, Albrecht
; Hofmann, Bernd
; Tautenhahn, Ulrich
; Yamamoto, Masahiro
: Convergence rates for Tikhonov regularization from different kinds of smoothness conditions
The paper is concerned with
ill-posed operator equations $Ax=y$ where $A:X \to Y$ is an
injective bounded linear operator with non-closed range
$R(A)$ and $X$ and $Y$ are Hilbert spaces. The solution $x=x^\dagger$ is assumed to be in the range $R(G)$ of some selfadjoint strictly positive bounded linear operator $G:X \to X$. Under several assumptions on $G$, such as $G=\varphi(A^*A)$
or more generally $R(G) \subset R(\varphi(A^*A))$,
inequalities of the form $\rho^2(G) \le A^*A$, or range inclusions $R(\rho(G)) \subset R(|A|)$, convergence rates for the regularization error $\|x_{\alpha} - x^\dagger\|$ of Tikhonov regularization are established. We also show that part of our assumptions automatically imply so-called source conditions. The paper contains a series of new
results but also intends to uncover cross-connections between the different kinds of smoothness conditions that have been discussed in the literature on convergence rates for Tikhonov
regularization.
Keywords:
linear ill-posed problems, Tikhonov regularization, convergence rates, smoothness conditions, index functions, operator monotone functions, range inclusions