Quasi-Newton iterative solution approaches for nonsmooth elliptic operators with applications to elasto-plasticity

This paper is devoted to the extension of a quasi-Newton/variable preconditioning (QNVP) method to non-smooth problems, motivated by elasto-plastic models. Two approaches are discussed: the first one is carried out via regularized approximations of the nonsmooth problem, and the second one gives an extension to nonsmooth operators in order to be applied directly. Convergence analysis is presented for both variants. Then these abstract methods are applied to elasto-plasticity where two different variants of QNVP are investigated and combined with the deflated conjugate gradient and aggregation-based algebraic multigrid methods. The convergence results are illustrated on numerical examples in 3D inspired by real-life problems, and they demonstrate that the suggested QNVP methods are competitive with the standard Newton method. Well-documented Matlab codes on elasto-plasticity are used and enriched by the suggested methods.