Abstract
We introduce a new numerical method, based on Bernoulli polynomials, for solving multiterm variable-order fractional differential equations. The variable-order fractional derivative was considered in the Caputo sense, while the Riemann–Liouville integral operator was used to give approximations for the unknown function and its variable-order derivatives. An operational matrix of variable-order fractional integration was introduced for the Bernoulli functions. By assuming that the solution of the problem is sufficiently smooth, we approximated a given order of its derivative using Bernoulli polynomials. Then, we used the introduced operational matrix to find some approximations for the unknown function and its derivatives. Using these approximations and some collocation points, the problem was reduced to the solution of a system of nonlinear algebraic equations. An error estimate is given for the approximate solution obtained by the proposed method. Finally, five illustrative examples were considered to demonstrate the applicability and high accuracy of the proposed technique, comparing our results with the ones obtained by existing methods in the literature and making clear the novelty of the work. The numerical results showed that the new method is efficient, giving high-accuracy approximate solutions even with a small number of basis functions and when the solution to the problem is not infinitely differentiable, providing better results and a smaller number of basis functions when compared to state-of-the-art methods.
Highlights
In the last few decades, fractional calculus has attracted the attention of many scientists in different fields such as mathematics, physics, chemistry, and engineering
Due to the fact that fractional operators consider the evolution of the system, by taking the global correlation, and local characteristics, some physical phenomena are better described by fractional derivatives [1]
A recent generalization of the theory of fractional calculus is to allow the fractional order of the derivatives to be dependent on time, i.e., to be nonconstant or of variable order
Summary
In the last few decades, fractional calculus has attracted the attention of many scientists in different fields such as mathematics, physics, chemistry, and engineering. Many researchers have introduced and developed numerical methods in order to obtain approximated solutions for this class of equations. We employ a spectral method based on Bernoulli polynomials in order to obtain numerical solutions to the problem (1) and (2). To the best of our knowledge, this is the first time in the literature that such a method for solving a general class of multiterm variable-order FDEs based on the Riemann–Liouville fractional integral of the basis vector has been introduced.
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