Solution of underdetermined nonlinear equations by stationary iteration methods

Abstract

Nonlinear stationary fixed point iterations inR n are considered. The Perron-Ostrowski theorem [23] guarantees convergence if the iteration functionG possesses an isolated fixed pointu. In this paper a sufficient condition for convergence is given ifG possesses a manifold of fixed points. As an application, convergence of a nonlinear extension of the method of Kaczmarz is proved. This method is applicable to underdetermined equations; it is appropriate for the numerical treatment of large and possibly ill-conditioned problems with a sparse, nonsquare Jacobian matrix. A practical example of this type (nonlinear image reconstruction in ultrasound tomography) is included.