Discretization of Linear Problems in Banach Spaces: Residual Minimization, Nonlinear Petrov{Galerkin, and Monotone Mixed Methods I. Muga† · K.G. van der Zee‡ 5th June, 2018 Abstract This work presents a comprehensive discretization theory for abstract linear operator equations in Banach spaces. The fundamental starting point of the theory is the idea of residual minimization in dual norms, and its inex- act version using discrete dual norms. It is shown that this development, in the case of strictly-convex reflexive Banach spaces with strictly-convex dual, gives rise to a class of nonlinear Petrov{Galerkin methods and, equiv- alently, abstract mixed methods with monotone nonlinearity. Crucial in the formulation of these methods is the (nonlinear) bijective duality map. Under the Fortin condition, we prove discrete stability of the abstract inexact method, and subsequently carry out a complete error analysis. As part of our analysis, we prove new bounds for best-approximation projec- tors, which involve constants depending on the geometry of the underlying Banach space. The theory generalizes and extends the classical Petrov{ Galerkin method as well as existing residual-minimization approaches, such as the discontinuous Petrov{Galerkin method. Keywords Operators in Banach spaces · Residual minimization · Petrov{Galerkin discretization · Error analysis · Quasi-optimality · Duality mapping · Best approximation · Geometric constants Mathematics Subject Classification 41A65 · 65J05 · 46B20 · 65N12 · 65N15 arXiv:1511.04400v3 [math.NA] 29 Jul 2018 †Pontificia Univ. Cat´olicade Valpara´ıso,Instituto de Mathem´aticas,
[email protected] ‡University of Nottingham, School of Mathematical Sciences,
[email protected] 1 Contents 1 Introduction3 1.1 Petrov{Galerkin discretization and residual minimization .