10 research outputs found
The Galerkin Finite Element Method for A Multi-term Time-Fractional Diffusion equation
We consider the initial/boundary value problem for a diffusion equation
involving multiple time-fractional derivatives on a bounded convex polyhedral
domain. We analyze a space semidiscrete scheme based on the standard Galerkin
finite element method using continuous piecewise linear functions. Nearly
optimal error estimates for both cases of initial data and inhomogeneous term
are derived, which cover both smooth and nonsmooth data. Further we develop a
fully discrete scheme based on a finite difference discretization of the
time-fractional derivatives, and discuss its stability and error estimate.
Extensive numerical experiments for one and two-dimension problems confirm the
convergence rates of the theoretical results.Comment: 22 pages, 4 figure
Error Analysis of Semidiscrete Finite Element Methods for Inhomogeneous Time-Fractional Diffusion
We consider the initial boundary value problem for the inhomogeneous
time-fractional diffusion equation with a homogeneous Dirichlet boundary
condition and a nonsmooth right hand side data in a bounded convex polyhedral
domain. We analyze two semidiscrete schemes based on the standard Galerkin and
lumped mass finite element methods. Almost optimal error estimates are obtained
for right hand side data , , for both semidiscrete schemes. For lumped mass method, the optimal
-norm error estimate requires symmetric meshes. Finally, numerical
experiments for one- and two-dimensional examples are presented to verify our
theoretical results.Comment: 21 pages, 4 figure
Numerical reconstruction of the spatial component in the source term of a time-fractional diffusion equation
In this article, we are concerned with the analysis on the numerical
reconstruction of the spatial component in the source term of a time-fractional
diffusion equation. This ill-posed problem is solved through a stabilized
nonlinear minimization system by an appropriately selected Tikhonov
regularization. The existence and the stability of the optimization system are
demonstrated. The nonlinear optimization problem is approximated by a fully
discrete scheme, whose convergence is established under a novel result verified
in this study that the -norm of the solution to the discrete forward
system is uniformly bounded. The iterative thresholding algorithm is proposed
to solve the discrete minimization, and several numerical experiments are
presented to show the efficiency and the accuracy of the algorithm.Comment: 17 pages, 2 figures, 2 table
Convergence analysis of a Crank-Nicolson Galerkin method for an inverse source problem for parabolic equations with boundary observations
This work is devoted to an inverse problem of identifying a source term
depending on both spatial and time variables in a parabolic equation from
single Cauchy data on a part of the boundary. A Crank-Nicolson Galerkin method
is applied to the least squares functional with an quadratic stabilizing
penalty term. The convergence of finite dimensional regularized approximations
to the sought source as measurement noise levels and mesh sizes approach to
zero with an appropriate regularization parameter is proved. Moreover, under a
suitable source condition, an error bound and corresponding convergence rates
are proved. Finally, several numerical experiments are presented to illustrate
the theoretical findings.Comment: Inverse source problem, Tikhonov regularization, Crank-Nicolson
Galerkin method, Source condition, Convergence rates, Ill-posedness,
Parabolic proble
NUMERICAL RECONSTRUCTION OF HEAT FLUXES ∗
Abstract. This paper studies the reconstruction of heat fluxes on an inner boundary of a heat conductive system when the measurement of temperature in a small subregion near the outer boundary of the physical domain is available. We will first consider two different regularization formulations for this severely ill-posed inverse problem and justify their well-posedness; then we will propose two fully discrete finite element methods to approximate the resultant nonlinear minimization problems. The existence and uniqueness of the discrete minimizers and convergence of the finite element solution are rigorously demonstrated. A conjugate gradient method is formulated to solve the nonlinear finite element optimization problems. Numerical experiments are given to demonstrate the stability and effectiveness of the proposed reconstruction methods