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      Optimal Control of Time-Delay Fractional Equations via a Joint Application of Radial Basis Functions and Collocation Method

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          Abstract

          A novel approach to solve optimal control problems dealing simultaneously with fractional differential equations and time delay is proposed in this work. More precisely, a set of global radial basis functions are firstly used to approximate the states and control variables in the problem. Then, a collocation method is applied to convert the time-delay fractional optimal control problem to a nonlinear programming one. By solving the resulting challenge, the unknown coefficients of the original one will be finally obtained. In this way, the proposed strategy introduces a very tunable framework for direct trajectory optimization, according to the discretization procedure and the range of arbitrary nodes. The algorithm’s performance has been analyzed for several non-trivial examples, and the obtained results have shown that this scheme is more accurate, robust, and efficient than most previous methods.

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          A new collection of real world applications of fractional calculus in science and engineering

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            Waiting-times and returns in high-frequency financial data: an empirical study

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              Anomalous diffusion expressed through fractional order differential operators in the Bloch-Torrey equation.

              Diffusion weighted MRI is used clinically to detect and characterize neurodegenerative, malignant and ischemic diseases. The correlation between developing pathology and localized diffusion relies on diffusion-weighted pulse sequences to probe biophysical models of molecular diffusion-typically exp[-(bD)]-where D is the apparent diffusion coefficient (mm(2)/s) and b depends on the specific gradient pulse sequence parameters. Several recent studies have investigated the so-called anomalous diffusion stretched exponential model-exp[-(bD)(alpha)], where alpha is a measure of tissue complexity that can be derived from fractal models of tissue structure. In this paper we propose an alternative derivation for the stretched exponential model using fractional order space and time derivatives. First, we consider the case where the spatial Laplacian in the Bloch-Torrey equation is generalized to incorporate a fractional order Brownian model of diffusivity. Second, we consider the case where the time derivative in the Bloch-Torrey equation is replaced by a Riemann-Liouville fractional order time derivative expressed in the Caputo form. Both cases revert to the classical results for integer order operations. Fractional order dynamics derived for the first case were observed to fit the signal attenuation in diffusion-weighted images obtained from Sephadex gels, human articular cartilage and human brain. Future developments of this approach may be useful for classifying anomalous diffusion in tissues with developing pathology.
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                Author and article information

                Journal
                Entropy (Basel)
                Entropy (Basel)
                entropy
                Entropy
                MDPI
                1099-4300
                26 October 2020
                November 2020
                : 22
                : 11
                : 1213
                Affiliations
                [1 ]School of Science, Hunan City University, Yiyang 413000, China; shubo.chen@ 123456163.com
                [2 ]Faculty of Industry and Mining (khash), University of Sistan and Baluchestan, Zahedan 98155-987, Iran; soradizeid@ 123456eng.usb.ac.ir
                [3 ]Department of Mechanical Engineering, University of Manitoba, Winnipeg, MB R3T 5V6, Canada; jahanshahi.hadi90@ 123456gmail.com
                [4 ]Research Group in Electronic, Biomedical and Telecommunication Engineering, University of Castilla-La Mancha (UCLM), 16071 Cuenca, Spain
                [5 ]CONACyT-Tecnológico Nacional de México/CENIDET, Interior Internado Palmira S/N, Col. Palmira, Cuernavaca C.P. 62490, Morelos, Mexico; jose.ga@ 123456cenidet.tecnm.mx
                [6 ]Department of Economics, European University Institute, Via delle Fontanelle, 18, I-50014 Florence, Italy; stelios.bekiros@ 123456eui.eu
                [7 ]Rimini Centre for Economic Analysis (RCEA), LH3079, Wilfrid Laurier University, 75 University Ave W., Waterloo, ON N2L3C5, Canada
                [8 ]Department of Mathematics, Huzhou University, Huzhou 313000, China
                [9 ]Hunan Provincial Key Laboratory of Mathematical Modeling and Analysis in Engineering, Changsha University of Science & Technology, Changsha 410114, China
                Author notes
                Author information
                https://orcid.org/0000-0001-5918-915X
                https://orcid.org/0000-0002-0942-3638
                https://orcid.org/0000-0001-9403-3767
                https://orcid.org/0000-0002-0944-2134
                Article
                entropy-22-01213
                10.3390/e22111213
                7711967
                33286981
                60ed3740-3200-4792-b303-099ee4466ed8
                © 2020 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 02 September 2020
                : 14 October 2020
                Categories
                Article

                fractional optimal control problem,delay system,radial basis function,direct optimization,collocation points,nonlinear programming problem

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