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Erschienen in:
19.05.2017
Optimal Error Analysis of a FEM for Fractional Diffusion Problems by Energy Arguments
Erschienen in: Journal of Scientific Computing | Ausgabe 1/2018
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Abstract
In this article, the piecewise-linear finite element method (FEM) is applied to approximate the solution of time-fractional diffusion equations on bounded convex domains. Standard energy arguments do not provide satisfactory results for such a problem due to the low regularity of its exact solution. Using a delicate energy analysis, a priori optimal error bounds in \(L^2(\varOmega )\)-, \(H^1(\varOmega )\)-norms, and a quasi-optimal bound in \(L^{\infty }(\varOmega )\)-norm are derived for the semidiscrete FEM for cases with smooth and nonsmooth initial data. The main tool of our analysis is based on a repeated use of an integral operator and use of a \(t^m\) type of weights to take care of the singular behavior of the continuous solution at \(t=0\). The generalized Leibniz formula for fractional derivatives is found to play a key role in our analysis. Numerical experiments are presented to illustrate some of the theoretical results.