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Monotonicity results for delta fractional differences revisited

  • Lynn Erbe , Christopher S. Goodrich , Baoguo Jia and Allan Peterson EMAIL logo
From the journal Mathematica Slovaca

Abstract

In this paper, by means of a recently obtained inequality, we study the delta fractional difference, and we obtain the following interrelated theorems, which improve recent results in the literature.

Theorem A

Assume that f : ℕa → ℝ and thatΔaνf(t) ≥ 0, for eacht ∈ ℕa+2−ν, with 1 < ν < 2. Iff(a+1)νk+2f(a),for each k ∈ ℕ0, then Δ f(t) ≥ 0 for t ∈ ℕa+1.

Theorem B

Assume that f : ℕa → ℝ and thatΔaνf(t) ≥ 0, for each t ∈ ℕa+2−ν, with 1 < ν < 2. If

f(a+2)νk+1f(a+1)+(k+1ν)ν(k+2)(k+3)f(a)
for each k ∈ ℕ1, then Δ f(t) ≥ 0 for t ∈ ℕa+2.

Theorem C

Assume that f : ℕa → ℝ and thatΔaνf(t) ≥ 0, for each t ∈ ℕa+2−ν, with 1 < ν < 2. If

f(a+3)νkf(a+2)+(kν)νk(k+1)f(a+1)+(k+1ν)(kν)ν(k+2)(k+1)kf(a)
for k ∈ ℕ2, then Δ f(t) ≥ 0, fort ∈ ℕa+3.

In addition, we obtain the following result, which extends a recent result due to Atici and Uyanik.

Theorem D

Assume that f : ℕa → ℝ, ΔNf(t) ≥ 0 for t ∈ ℕa, and (−1)NiΔif(a) ≤ 0 fori = 0, 1, …, N − 1. ThenΔaνf(t) ≥ 0 fort ∈ ℕa+Nν.


(Communicated by Ján Borsík)

The third author, B. Jia, was supported by The National Natural Science Foundation of China (No.11271380) and Guangdong Province Key Laboratory of Computational Science.

Acknowledgement

The authors would like to thank the two anonymous referees for their useful suggestions and comments.

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Received: 2015-6-1
Accepted: 2016-1-22
Published Online: 2017-7-14
Published in Print: 2017-8-28

© 2017 Mathematical Institute Slovak Academy of Sciences

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