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Author: search.filters.author.Kittisopaporn, AdisornSubject: search.filters.subject.Gradient descent

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    Approximate solutions of the 2D space-time fractional diffusion equation via a gradient-descent iterative algorithm with Grünwald-Letnikov approximation
    (2022-01-01)
    Kittisopaporn, Adisorn
    ;
    Chansangiam, Pattrawut
    We consider the two-dimensional space-time fractional differential equation with the Caputo’s time derivative and the Riemann-Liouville space derivatives on bounded domains. The equation is subjected to the zero Dirichlet boundary condition and the zero initial condition. We discretize the equation by finite difference schemes based on Grünwald-Letnikov approximation. Then we linearize the discretized equations into a sparse linear system. To solve such linear system, we propose a gradient-descent iterative algorithm with a sequence of optimal convergence factor aiming to minimize the error occurring at each iteration. The convergence analysis guarantees the capability of the algorithm as long as the coefficient matrix is invertible. In addition, the convergence rate and error estimates are provided. Numerical experiments demonstrate the efficiency, the accuracy and the performance of the proposed algorithm.
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    Approximated least-squares solutions of a generalized Sylvester-transpose matrix equation via gradient-descent iterative algorithm
    (2021-12-01)
    Kittisopaporn, Adisorn
    ;
    Chansangiam, Pattrawut
    This paper proposes an effective gradient-descent iterative algorithm for solving a generalized Sylvester-transpose equation with rectangular matrix coefficients. The algorithm is applicable for the equation and its interesting special cases when the associated matrix has full column-rank. The main idea of the algorithm is to have a minimum error at each iteration. The algorithm produces a sequence of approximated solutions converging to either the unique solution, or the unique least-squares solution when the problem has no solution. The convergence analysis points out that the algorithm converges fast for a small condition number of the associated matrix. Numerical examples demonstrate the efficiency and effectiveness of the algorithm compared to renowned and recent iterative methods.
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    Gradient-descent iterative algorithm for solving a class of linear matrix equations with applications to heat and Poisson equations
    (2020-12-01)
    Kittisopaporn, Adisorn
    ;
    Chansangiam, Pattrawut
    In this paper, we introduce a new iterative algorithm for solving a generalized Sylvester matrix equation of the form ∑t=1pAtXBt=C which includes a class of linear matrix equations. The objective of the algorithm is to minimize an error at each iteration by the idea of gradient-descent. We show that the proposed algorithm is widely applied to any problems with any initial matrices as long as such problem has a unique solution. The convergence rate and error estimates are given in terms of the condition number of the associated iteration matrix. Furthermore, we apply the proposed algorithm to sparse systems arising from discretizations of the one-dimensional heat equation and the two-dimensional Poisson’s equation. Numerical simulations illustrate the capability and effectiveness of the proposed algorithm comparing to well-known methods and recent methods.