New preconditioner updates in Newton-Krylov methods for nonlinear systems

We address the problem of preconditioning sequences of large sparse indefinite systems of linear equations arising in the solution of large nonlinear systems via Newton-Krylov methods. We present two new strategies to construct approximate updates of a factorized preconditioner for a reference matrix of the sequence. Both updates are based on the availability of an incomplete factorization for one matrix of the sequence and differ in the approximation of the so-called ideal updates. Furthermore, nearly matrix-free implementations are discussed.