Time‐Dependent Term Identification in the Time–Space Fractional Derivative Diffusion Equation From Integral Over Specified Condition

ABSTRACT In this paper, a time–space fractional order inverse source problem to determine the temperature solution and the time‐dependent source term from heat moment to the time–space fractional heat equation with an initial condition, homogeneous Dirichlet boundary conditions, and integral overdetermination condition is investigated. Two unconditionally stable finite difference schemes are proposed to find a numerical solution of the direct problem. Namely, method I is based on the approximation of the time‐fractional derivative via Laplace transformation, whereas method II is based on finite difference approximation. The inverse problem is solved iteratively by lsqnonlin routine from the MATLAB optimization toolbox after reformatting the problem to a minimization of an objective functional imposed from the overdetermination condition. Since the problem under consideration is generally ill‐posed, Tikhonov's method is used to get a uniform, stable, and accurate result. Several numerical test examples explain that the proposed methods are stable and work satisfactorily for various amounts of noise levels.