Volume 52, Number 2, March–April 2018
|Page(s)||773 - 801|
|Published online||20 July 2018|
Error analysis of a FVEM for fractional order evolution equations with nonsmooth initial data★
Department of Mathematics and Statistics, Sultan Qaboos University,
2 Department of Mathematics, Industrial Mathematics Group, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
* Corresponding author: firstname.lastname@example.org
Accepted: 30 April 2018
In this paper, a finite volume element (FVE) method is considered for spatial approximations of time fractional diffusion equations involving a Riemann-Liouville fractional derivative of order α ∈ (0, 1) in time. Improving upon earlier results [Karaa et al., IMA J. Numer. Anal. 37 (2017) 945–964], error estimates in L2 (Ω)- and H1 (Ω)-norms for the semidiscrete problem with smooth and mildly smooth initial data, i.e., v ∈ H2(Ω) ∩ H01(Ω) and v ∈ H01(Ω) are established. For nonsmooth data, that is, v ∈ L2 (Ω), the optimal L2 (Ω)-error estimate is shown to hold only under an additional assumption on the triangulation, which is known to be satisfied for symmetric triangulations. Superconvergence result is also proved and as a consequence, a quasi-optimal error estimate is established in the L∞ (Ω)-norm. Further, two fully discrete schemes using convolution quadrature in time generated by the backward Euler and the second-order backward difference methods are analyzed, and error estimates are derived for both smooth and nonsmooth initial data. Based on a comparison of the standard Galerkin finite element solution with the FVE solution and exploiting tools for Laplace transforms with semigroup type properties of the FVE solution operator, our analysis is then extended in a unified manner to several time fractional order evolution problems. Finally, several numerical experiments are conducted to confirm our theoretical findings.
Mathematics Subject Classification: 65M60 / 65M12 / 65M15
Key words: Fractional order evolution equation / subdiffusion / finite volume element method / Laplace transform / backward Euler and second-order backward difference methods / convolution quadrature / optimal error estimate / smooth and nonsmooth data
© EDP Sciences, SMAI 2018
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