Multigrid with rough coefficients and Multiresolution operator decomposition from Hierarchical Information Games

TL;DR

This paper presents a novel multigrid method for PDEs with rough coefficients, based on a game theory approach that constructs hierarchical basis functions (gamblets) enabling efficient, parallelizable solutions with rigorous accuracy guarantees.

Contribution

It introduces a new multigrid framework using a decision/game theory formulation to create orthogonal multiresolution basis functions for PDEs with rough coefficients, achieving near-linear complexity.

Findings

Achieves near-linear complexity for PDEs with rough coefficients.

Provides a hierarchical basis (gamblets) with exponential decay properties.

Enables parallel computation and sparse solution compression.

Abstract

We introduce a near-linear complexity (geometric and meshless/algebraic) multigrid/multiresolution method for PDEs with rough ($L^\infty$) coefficients with rigorous a-priori accuracy and performance estimates. The method is discovered through a decision/game theory formulation of the problems of (1) identifying restriction and interpolation operators (2) recovering a signal from incomplete measurements based on norm constraints on its image under a linear operator (3) gambling on the value of the solution of the PDE based on a hierarchy of nested measurements of its solution or source term. The resulting elementary gambles form a hierarchy of (deterministic) basis functions of $H^1_0(\Omega)$ (gamblets) that (1) are orthogonal across subscales/subbands with respect to the scalar product induced by the energy norm of the PDE (2) enable sparse compression of the solution space in $H^1_0(\Omega)$ (3) induce an orthogonal multiresolution operator decomposition. The operating diagram of the multigrid method is that of an inverted pyramid in which gamblets are computed locally (by virtue of their exponential decay), hierarchically (from fine to coarse scales) and the PDE is decomposed into a hierarchy of independent linear systems with uniformly bounded condition numbers. The resulting algorithm is parallelizable both in space (via localization) and in bandwith/subscale (subscales can be computed independently from each other). Although the method is deterministic it has a natural Bayesian interpretation under the measure of probability emerging (as a mixed strategy) from the information game formulation and multiresolution approximations form a martingale with respect to the filtration induced by the hierarchy of nested measurements.