Tomáš Kisela

Discrete Mittag-Leffler Functions in Linear Fractional Difference Equations

This paper investigates some initial value problems in discrete fractional calculus. We introduce a linear difference equation of fractional order along with suitable initial conditions of fractional type and prove the existence and uniqueness of the solution. Then the structure of the solutions space is discussed, and, in a particular case, an explicit form of the general solution involving discrete analogues of Mittag-Leffler functions is presented. All our observations are performed on a special time scale which unifies and generalizes ordinary difference calculus and 𝑞-difference calculus. Some of our results are new also in these particular discrete settings.

Stability regions for linear fractional differential systems and their discretizations

This paper concerns with basic stability properties of linear autonomous fractional differential and difference systems involving derivative operators of the Riemann-Liouville type. We derive stability regions for special discretizations of the studied fractional differential systems including a precise description of their asymptotics. Our analysis particularly shows that discretizations based on backward differences can retain the key qualitative properties of underlying fractional differential systems. In addition, we introduce the backward discrete Laplace transform and employ some of its properties as the main proof tool.

Stability and asymptotic properties of a linear fractional difference equation

AbstractThis paper discusses qualitative properties of the two-term linear fractional difference equation ∇α0y(n)=λy(n), where α,λ∈R, 0<α<1, λ≠1 and ∇α0 is the α th order Riemann-Liouville difference operator. For this purpose, we show that this fractional equation is the Volterra equation of convolution type. This enables us to analyse its qualitative properties by use of tools standardly employed in the qualitative investigation of Volterra difference equations. As the main result, we derive a sharp condition for the asymptotic stability of the studied equation and, moreover, give a precise asymptotic description of its solutions.MSC:39A30, 39A12, 26A33.

Power functions and essentials of fractional calculus on isolated time scales

This paper is concerned about a recently suggested axiomatic definition of power functions on a general time scale and its consequences to fractional calculus. Besides a discussion of the existence and uniqueness of such functions, we derive an efficient formula for the computation of power functions of rational orders on an arbitrary isolated time scale. It can be utilized in the introduction and evaluation of fractional sums and differences. We also deal with the Laplace transform of such fractional operators, which, apart from solving of fractional difference equations, enables a more detailed comparison of our results with those in the relevant literature. Some illustrating examples (including special fractional initial value problems) are presented as well.MSC:26E70, 39A12, 26A33, 44A10.

Exact and discretized stability of the Bagley–Torvik equation

Abstract The paper discusses stability and asymptotic properties of a two-term linear fractional differential equation involving the Bagley–Torvik equation as the particular case. These properties are analysed for the exact as well as numerical solutions obtained from the Grunwald–Letnikov discretization of the studied differential equation. As the main results, precise descriptions of the exact and discretized stability regions are presented, including the decay rate of the solutions. These results enable us, among others, to observe similarities and distinctions between the asymptotic behaviour of the classical and fractional damping models.

Fractional differential equations with a constant delay

The paper discusses stability and asymptotic properties of a fractional-order differential equation involving both delayed as well as non-delayed terms. As the main results, explicit necessary and sufficient conditions guaranteeing asymptotic stability of the zero solution are presented, including asymptotic formulae for all solutions. The studied equation represents a basic test equation for numerical analysis of delay differential equations of fractional type. Therefore, the knowledge of optimal stability conditions is crucial, among others, for numerical stability investigations of such equations. Theoretical conclusions are supported by comments and comparisons distinguishing behaviour of a fractional-order delay equation from its integer-order pattern.

Asymptotic Stability Of Dynamic Equations With Two Fractional Terms: Continuous Versus Discrete Case

Abstract The paper discusses asymptotic stability conditions for the linear fractional difference equation ∇αy(n) + a∇βy(n) + by(n) = 0 with real coefficients a, b and real orders α > β > 0 such that α/β is a rational number. For given α, β, we describe various types of discrete stability regions in the (a, b)-plane and compare them with the stability regions recently derived for the underlying continuous pattern Dαx(t) + aDβx(t) + bx(t) = 0 involving two Caputo fractional derivatives. Our analysis shows that discrete stability sets are larger and their structure much more rich than in the case of the continuous counterparts.