*Article* **Generalized Bessel Polynomial for Multi-Order Fractional Differential Equations**

**Mohammad Izadi 1,\* and Carlo Cattani 2**


Received: 19 May 2020; Accepted: 6 July 2020; Published: 30 July 2020

**Abstract:** The main goal of this paper is to define a simple but effective method for approximating solutions of multi-order fractional differential equations relying on Caputo fractional derivative and under supplementary conditions. Our basis functions are based on some original generalization of the Bessel polynomials, which satisfy many properties shared by the classical orthogonal polynomials as given by Hermit, Laguerre, and Jacobi. The main advantages of our polynomials are two-fold: All the coefficients are positive and any collocation matrix of Bessel polynomials at positive points is strictly totally positive. By expanding the unknowns in a (truncated) series of basis functions at the collocation points, the solution of governing differential equation can be easily converted into the solution of a system of algebraic equations, thus reducing the computational complexities considerably. Several practical test problems also with some symmetries are given to show the validity and utility of the proposed technique. Comparisons with available exact solutions as well as with several alternative algorithms are also carried out. The main feature of our approach is the good performance both in terms of accuracy and simplicity for obtaining an approximation to the solution of differential equations of fractional order.

**Keywords:** caputo fractional derivative; bessel functions; collocation method; multi-order fractional differential equations

**JEL Classification:** 26A33; 65L60; 42C05; 65L05
