On τ-preconditioner for a novel fourth-order difference scheme of two-dimensional Riesz space-fractional diffusion equations
Computers & Mathematics with Applications(2023)
Abstract
In this paper, a τ-preconditioner for a novel fourth-order finite difference scheme of two-dimensional Riesz space-fractional diffusion equations (2D RSFDEs) is considered, in which a fourth-order fractional centered difference operator is adopted for the discretizations of spatial Riesz fractional derivatives, while the Crank-Nicolson method is adopted to discretize the temporal derivative. The scheme is proven to be unconditionally stable and has a convergence rate of O(Δt2+Δx4+Δy4) in the discrete L2-norm, where Δt, Δx and Δy are the temporal and spatial step sizes, respectively. In addition, the preconditioned conjugate gradient (PCG) method with τ-preconditioner is applied to solve the discretized symmetric positive definite linear systems arising from 2D RSFDEs. Theoretically, we show that the τ-preconditioner is invertible by a new technique, and analyze the spectrum of the corresponding preconditioned matrix. Moreover, since the τ-preconditioner can be diagonalized by the discrete sine transform matrix, the total operation cost of the PCG method is O(NxNylogNxNy), where Nx and Ny are the number of spatial unknowns in x- and y-directions. Finally, numerical experiments are performed to verify the convergence orders, and show that the PCG method with the τ-preconditioner for solving the discretized linear system has a convergence rate independent of discretization stepsizes.
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Key words
Riesz space-fractional diffusion equations,τ-preconditioner,Stability and convergence,Spectral analysis,Preconditioned conjugate gradient method
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