یک روش عناصر متناهی کارا برای مسائل کنترل بهینه شامل معادلات پخش زمان–کسری مرتبه توزیع‌شده

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه ریاضی کاربردی، دانشکده علوم ریاضی، دانشگاه کاشان، کاشان، ایران

2 دانشکده ریاضی و علوم کامپیوتر، دانشگاه صنعتی امیرکبیر، تهران، ایران

چکیده

در این مقاله، یک روش عناصر متناهی برای تقریب جواب مسائل کنترل بهینه شامل معادلات پخش زمان-کسری مرتبه توزیع شده، معرفی می‌کنیم. دینامیک این مسائل شامل مشتقات زمان-کسری از مرتبه توزیع شده می‌باشد که تعمیمی از مشتقات کسری هستند. علیرغم اهمیت این مسائل، تحقیقات کمی در مورد حل آنها در منابع وجود دارد. روش‌های عددی برای حل مسائل کنترل بهینه به دو دسته کلی روش‌های غیرمستقیم و روش‌های مستقیم تقسیم می‌شوند. در روش‌های غیرمستقیم با استفاده از اصل پونتریاگین، شرایط لازم برای بهینگی به دست آمده و به صورت یک مساله مقدار مرزی دو نقطه‌ای غیرخطی بازنویسی می‌شود. از طرف دیگر، در روش‌های مستقیم با گسسته‌سازی متغیرهای کنترل و وضعیت، مساله مورد نظر به یک مساله برنامه‌ریزی غیرخطی تقلیل می‌یابد. به دلیل مشکلات مربوط به حل دستگاه معادلات حاصل از شرایط لازم برای بهینگی در مسائل کنترل بهینه شامل معادلات پخش زمان-کسری مرتبه توزیع شده، در این مقاله از دیدگاه روش‌های مستقیم برای تقریب جواب این مسائل استفاده می‌کنیم. به منظور تقریب مشتقات زمان-کسری مرتبه توزیع شده، رو‌ش‌های تقریبی گرانوالد-لتنیکف و L1 را مورد استفاده قرار داده و دو فرمول تقریبی برای مشتق به دست می‌آوریم. همچنین برای گسسته‌سازی مکانی از روش عناصر متناهی تکه‌ای خطی استفاده می‌کنیم. به این ترتیب، مساله اصلی را به یک مساله بهینه‌سازی درجه دو محدب تبدیل می‌کنیم که می‌تواند توسط الگوریتم‌های بهینه‌سازی موجود به طور کارا حل شود. برای اثبات کارایی و دقت روش ارئه شده، دو مثال عددی در نظر می‌گیریم.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

An Efficient Finite Element Method for Optimal Control Problems Involving Distributed-Order Time-Fractional Diffusion Equations

نویسندگان [English]

  • Roya Vaziri Doghezlou 1
  • Hamid Reza Tabrizidouz 1
  • Mostafa Shamsi 2
1 Department of Applied Mathematics, Faculty of Mathematical Science, University of Kashan, Kashan, Iran
2 Department of Mathematics and Computer Science, Amirkabir University of Technology, Tehran, Iran
چکیده [English]

In this paper, we present a finite element method to approximate the solution of optimal control problems involving distributed-order time-fractional diffusion equations. The dynamics of these problems involve distributed-order time-fractional derivatives, which are a generalization of fractional derivatives. Despite the importance of these problems, there exist few researches on their solving in the literatures. Numerical methods for solving optimal control problems are classified into two main categories, namely, indirect methods and direct methods. In the indirect methods, by using Pontryagin principle, the necessary conditions for optimality are derived and formulated as a nonlinear two-point boundary value problem. On the other hand, in the direct methods, by discretizing the control and state variables, the considered problem is reduced to a nonlinear programming problem. Due to the difficulties related to solving the system of equations resulting from the necessary conditions for optimality in optimal control problems involving distributed-order time-fractional diffusion equations, in this paper we use the approach of direct methods to approximate the solution of these problems. To approximate the distributed-order time-fractional derivatives, we employ the Grunwald-Letnikov and L1 approximation methods and derive two approximation formulas for derivative. Also for spatial discretization, we utilize the piecewise linear finite element method. Therefore, we transform the original problem into a convex quadratic optimization problem, which can be efficiently solved using existing optimization algorithms. We consider two numerical examples to demonstrate the efficiency and accuracy of the proposed method.

کلیدواژه‌ها [English]

  • Optimaⅼ ⅽontroⅼ probⅼems invoⅼving ⅾistributeⅾ−orⅾer time−fraⅽtionaⅼ ⅾiffusion equations
  • Ⅾireⅽt methoⅾs
  • Grünwaⅼⅾ−Ⅼetnikov
  • Finite eⅼement
  • approximation formuⅼas for ⅾerivative
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