## Convergence rates for regularization with sparsity constraints

Ronny Ramlau and Elena Resmerita

### Abstract

Tikhonov regularization with $p$-powers of the weighted $\ell_p$ norms as penalties, with $p\in (1,2)$, have been employed recently in reconstruction of sparse solutions of ill-posed inverse problems. This paper shows convergence rates for such a regularization with respect to the norm of the weighted spaces by assuming that the solutions satisfy a certain smoothness (source) condition. The meaning of the latter is analyzed in some detail. Moreover, converse results are established: Linear convergence rates for the residual, together with convergence of the approximations to the solution, can be achieved only if the solution satisfies a source condition. Further insights for the particular case of a convolution equation are provided by analyzing the equation both theoretically and numerically.

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### Key words

ill-posed problem, regularization, Bregman distance, sparsity

47A52, 65J20

### Links to the cited ETNA articles

 [19] Vol. 30 (2008), pp. 54-74 Ronny Ramlau: Regularization properties of Tikhonov regularization with sparsity constraints