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On improvements of the Rozanova's inequality
Journal of Inequalities and Applications volume 2011, Article number: 33 (2011)
Abstract
In the present paper, we establish some new Rozanova's type integral inequalities involving higher-order partial derivatives. The results in special cases yield some of the interrelated results on Rozanova's inequality and provide new estimates on inequalities of this type.
MS (2000) Subject Classifiication: 26D15.
1 Introduction
In the year 1960, Opial [1] established the following integral inequality:
Theorem A Suppose f ∈ C1[0, h] satisfies f(0) = f(h) = 0 and f(x) > 0 for all x ∈ (0, h). Then
The first Opial's type inequality was established by Willett [2] as follows:
Theorem B Let x(t) be absolutely continuous in [0, a], and x(0) = 0. Then
A non-trivial generalization of Theorem B was established by Hua [3] as follows:
Theorem C Let x(t) be absolutely continuous in [0, a], and x(0) = 0. Futher, let l be a positive integer. Then
A sharper inequality was established by Godunova [4] as follows:
Theorem D Let f(t) be convex and increasing functions on [0, ∞) with f(0) = 0. Further, let x(t) be absolutely continuous on [0, τ], and x(α) = 0. Then, following inequality holds
Rozanova [5] proved an extension of inequality (1.4) is embodied in the following:
Theorem F Let f(t) and g(t) be convex and increasing functions on [0, ∞) with f(0) = 0, and let p(t) ≥ 0, p'(t) > 0, t ∈ [α, a] with p(α) = 0. Further, let x(t) be absolutely continuous on [α, a), and x(α) = 0. Then, following inequality holds
The inequality (1.5) will be called as Rozanova's inequality in the paper.
Opial's inequality and its generalizations, extensions and discretizations play a fundamental role in establishing the existence and uniqueness of initial and boundary value problems for ordinary and partial differential equations as well as difference equations [6–13]. For Opial-type integral inequalities involving high-order partial derivatives, see [14, 15]. For an extensive survey on these inequalities, see [16].
The first aim of the present paper is to establish the following Opial-type inequality involving higher-order partial derivatives, which is an extension of the Rozanova's inequality (1.5).
Theorem 1.1 Let f and g be convex and increasing functions on [0, ∞) with f(0) = 0, and let p(s, t) ≥ 0, , D1D2p(s, t) > 0, s ∈ [α, a], t ∈ [β, b] with p(s, β) = p(α, t) = p(α, β) = 0 and D1D2p(s, t) |t = τ= 0. Further, let x(s, t) be absolutely continuous on [α, a) × [β, b], and x(s, β) = x(α, t) = x(α, β) = 0. Then following inequality holds
We also prove the following Rozanova-type inequality involving higher-order partial derivatives.
Theorem 1.2 Assume that
-
(i)
f, g and x(s, t) are as in Theorem 1.1,
-
(ii)
p(s, t) is increasing on [0, a] × [0, b] with p(s, β) = p(α, t) = p(α, β) = 0,
-
(iii)
h is concave and increasing on [0, ∞),
-
(iv)
ϕ(t) is increasing on [0, a] with ϕ(0) = 0,
-
(v)
For ,
Then
where
and
2 Main results and proofs
Theorem 2.1 Let f and g be convex and increasing functions on [0, ∞) with f(0) = 0, and let p(s, t) ≥ 0, , D1D2p(s, t) > 0, s ∈ [α, a], t ∈ [β, b] with p(s, β) = p(α, t) = p(α, β) = 0 and D1D2p(s, t) |t = τ= 0. Further, let x(s, t) be absolutely continuous on [α, a) × [β, b], and x(s, β) = x(α, t) = x(α, β) = 0. Then, following inequality holds
Proof Let so that D1D2y(s, t) = |D1D2x(s, t)| and y(s, t) ≥ |x(s, t)|. Thus, from Jensen's integral inequality, we obtain
By using the inequality (2.2), we have
On the other hand
From (2.3) and (2.4), we have
This completes the proof.
Remark 2.2 Let x(s, t) reduce to s(t), and with suitable modifications in the proof of Theorem 2.1, then (2.1) becomes inequality (1.5) stated in Section 1.
Remark 2.3 Taking for g(x) = x in (2.1), then (2.1) becomes the following inequality.
Let x(s, t) reduce to s(t), and with suitable modifications, then (2.5) becomes inequality (1.4) stated in Section 1.
Remark 2.4 For f(t) = tl+1, l ≥ 0, the inequality (2.5) reduces to
In the right side of (2.6), by Hölder inequality with indices l + 1 and (l + 1)l, gives
Let x(s, t) reduce to s(t) and α = β = 0, then (2.7) becomes Hua's inequality (1.3) stated in Section 1.
Theorem 2.5 Assume that
-
(i)
f, g and x(s, t) are as in Theorem 2.1,
-
(ii)
p(s, t) is increasing on [0, a] × [0, b] with p(s, β) = p(α, t) = p(α, β) = 0,
-
(iii)
h is concave and increasing on [0, ∞),
-
(iv)
ϕ(t) is increasing on [0, a] with ϕ(0) = 0,
-
(v)
For ,
(2.8)
Then
where
and
Proof From (2.2), we easily obtain
From (2.8), (2.10-2.12) and Jensen's inequality(for concave function), hence
This completes the proof.
Remark 2.6 Let x(s, t) reduce to s(t), and with suitable modifications in the proof of Theorem 2.5, then (2.9) becomes the following inequality:
The inequality has been obtained by Rozanova in [17]. For and , the inequality (2.13) reduces to Polya's inequality (see [17]).
Remark 2.7 Taking for g(x) = x in (2.9), then (2.9) becomes the following interesting inequality.
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Acknowledgements
The authors express their deep gratitude to the referees for their many very valuable suggestions and comments. The research of Chang-Jian Zhao was supported by National Natural Science Foundation of China (10971205), and the research of Wing-Sum Cheung was partially supported by a HKU URC grant.
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C-JZ and W-SC jointly contributed to the main results Theorems 2.1 and 2.5. Both authors read and approved the final manuscript.
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Zhao, CJ., Cheung, WS. On improvements of the Rozanova's inequality. J Inequal Appl 2011, 33 (2011). https://doi.org/10.1186/1029-242X-2011-33
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DOI: https://doi.org/10.1186/1029-242X-2011-33