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Zbl 1204.39004
At ic i, Ferhan M.; Şengül, Sevgi
Modeling with fractional difference equations.
(English)
[J] J. Math. Anal. Appl. 369, No. 1, 1-9 (2010). ISSN 0022-247X

A fractional sum of a function $f$ is introduced as $$\Delta _{a}^{-\alpha}f(t)=\frac{1}{\Gamma (\alpha )}\sum_{s=a}^{t-\alpha }(t-s-1)^{(\alpha -1)}f(s),$$ where $a\in R,$ $\alpha >0$, $x^{(\alpha )}=\Gamma (x+1)/\Gamma (x-\alpha +1),$ $f$ is defined for $s=a\ (\text {mod }1),$ and $\Delta _{a}^{-\alpha }f$ is defined for $t=a+\alpha \ (\text {mod }1).$ Besides some previously known properties of the fractional sum, additional properties such as a Leibniz type formula and a summation by parts formula are derived. A simple fractional calculus of a variation problem is defined and its Euler-Lagrange equation is derived. As an application, a so called Gompertz fractional difference equation is introduced and solved in terms of a series.
[Sui Sun Cheng (Hsinchu)]
MSC 2000:
*39A12 Discrete version of topics in analysis
39A05 General theory of difference equations
26A33 Fractional derivatives and integrals (real functions)
34A08

Keywords: fractional difference equation; Leibniz formula; summation by parts; variational problem; Gompertz equation

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