Open Access

Hermite–Hadamard type inequalities for n-times differentiable and geometrically quasi-convex functions

SpringerPlus20165:524

https://doi.org/10.1186/s40064-016-2083-y

Received: 26 October 2015

Accepted: 31 March 2016

Published: 26 April 2016

Abstract

By Hölder’s integral inequality, the authors establish some Hermite–Hadamard type integral inequalities for n-times differentiable and geometrically quasi-convex functions.

Keywords

Hermite–Hadamard type inequalitygeometrically quasi-convex functionHölder integral inequality

Mathematics Subject Classification

Primary 26D15; Secondary 26A5126B1241A5549J52

Background

Let I be an interval on \({\mathbb {R}}=(-\infty ,\infty )\). A function \(f:I\rightarrow {\mathbb {R}}\) is said to be convex if
$$f(\lambda x+(1-\lambda )y)\le \lambda f(x)+ (1-\lambda )f(y)$$
(1)
for \(x,y\in I\) and \(\lambda \in [0,1]\). If the inequality (1) reverses, then f is said to be concave on I.
A function \(f:I\subseteq {\mathbb {R}}_+=(0,\infty )\rightarrow {\mathbb {R}}_+\) is said to be geometrically convex on I if
$$\begin{aligned} f\left(x^\lambda y^{1-\lambda }\right )\le \left[f(x)\right ]^\lambda \left[f(y)\right]^{1-\lambda } \end{aligned}$$
for \(x,y\in I\) and \(\lambda \in [0,1]\).
One of the most famous inequalities for convex functions is Hermite–Hadamard’s inequality: if \(f:I\subseteq {\mathbb {R}}\rightarrow {\mathbb {R}}\) is convex on an interval I of real numbers and \(a,b\in I\) with \(a<b\), then
$$\begin{aligned} f\biggl (\frac{a+b}{2}\biggl )\le \frac{1}{b-a}\int _a^b f(x){{\mathrm{d}}}x \le \frac{f(a)+f(b)}{2}; \end{aligned}$$
(2)
if f is concave on I, then the inequality (2) is reversed.

We now collect several Hermite–Hadamard type integral inequalities as follows.

Theorem 1

(Dragomir and Agarwal 1998) Let \(f:I^\circ \subseteq {\mathbb {R}}\rightarrow {\mathbb {R}}\) be a differentiable mapping on \(I^\circ \) and \(a,b\in I^\circ \) with \(a<b\). If \(|f'|\) is convex on [ab], then
$$\begin{aligned} \biggl |\frac{f(a)+f(b)}{2}-\frac{1}{b-a}\int _a^bf(x){{\mathrm{d}}}x\biggl |\le \frac{(b-a)\bigr [|f'(a)|+|f'(b)|\bigr ]}{8}. \end{aligned}$$

Theorem 2

(Xi and Qi 2013) Let \(f:I \subseteq {\mathbb {R}}_+\rightarrow {\mathbb {R}}\) be a differentiable function on \(I^\circ \) and \(a,b\in I^\circ \) with \(a<b\). If \(|f'|\) is geometrically convex on [ab], then
$$\begin{aligned} \biggl |\frac{1}{\ln b-\ln a}\int _a^b\frac{f(x)}{x}{{\mathrm{d}}}x-f\bigl (\sqrt{a b}\,\bigr )\biggl |\le \frac{\ln b-\ln a}{4}\Bigl \{L\Bigl (\bigl [a|f'(a)|\bigr ]^{1/2},\bigl [b|f'(b)|\bigr ]^{1/2}\Bigr )\Bigl \}^2, \end{aligned}$$
where
$$\begin{aligned} L(u, v)=\frac{u-v}{\ln u-\ln v} \end{aligned}$$
for \(u,v>0\) and \(u\ne v\) is called the logarithmic mean.

Theorem 3

(Dragomir and Agarwal 1998) Let \(f:I^\circ \subseteq {\mathbb {R}}\rightarrow {\mathbb {R}}\) be a differentiable mapping on \(I^\circ \) and \(a,b\in I^\circ \) with \(a<b\). If \(|f'|^q\) for \(q\ge 1\) is convex on [ab], then
$$\begin{aligned} \biggl |\frac{f(a)+f(b)}{2}-\frac{1}{b-a}\int _a^bf(x){{\mathrm{d}}}x\biggl |\le \frac{b-a}{4}\biggl (\frac{|f'(a)|^q +|f'(b)|^q}{2}\biggr )^{1/q} \end{aligned}$$
and
$$\begin{aligned} \biggl |f\biggl (\frac{a+b}{2}\biggr )-\frac{1}{b-a}\int _a^bf(x){{\mathrm{d}}}x\biggl |\le \frac{b-a}{4}\biggl (\frac{|f'(a)|^q +|f'(b)|^q}{2}\biggr )^{1/q}. \end{aligned}$$

Theorem 4

(Kirmaci 2004) Let \(f:I\subseteq {\mathbb {R}}\rightarrow {\mathbb {R}}\) be differentiable on \(I^\circ \) and \(a,b\in I\) with \(a<b\). If \(|f'|^{p/(p-1)}\) for \(p>1\) is convex on [ab], then
$$\begin{aligned} \biggl |f\biggl (\frac{a+b}{2}\biggl )-\frac{1}{b-a}\int _a^bf(x){{\mathrm{d}}}x\biggl |\le \frac{b-a}{16}\biggl (\frac{4}{p+1}\biggl )^{1/p} \biggl \{\Bigr [|f'(a)|^{p/(p-1)}\\ +3|f'(b)|^{p/(p-1)}\Bigl ]^{1-1/p} +\Bigr [3|f'(a)|^{p/(p-1)}+|f'(b)|^{p/(p-1)}\Bigl ]^{1-1/p}\biggl \}. \end{aligned}$$

Corresponding to the concept of geometrically convex functions, the geometrically quasi-convex functions were introduced in Qi and Xi (2014) as follows.

Definition 1

(Definition 2.1 Qi and Xi 2014) A function \(f:I\subseteq {\mathbb {R}}_+\rightarrow {\mathbb {R}}_0=[0,\infty )\) is said to be geometrically quasi-convex function on I if
$$\begin{aligned} f\bigl (x^\lambda y^{1-\lambda }\bigr )\le \sup \{f(x),f(y)\} \end{aligned}$$
for \(x,y\in I\) and \(\lambda \in [0,1]\).

In Qi and Xi (2014), some integral inequalities of Hermite–Hadamard type for geometrically quasi-convex functions were established.

In recent years, some other kinds of Hermite–Hadamard type inequalities were generated. For more systematic information, please refer to Bai et al. (2012), Pearce and Pečarić (2000), Pečarić and Tong (1991), Wang and Qi (2013), Wang et al. (2012), Xi et al. (2012) and related references therein.

The aim of this paper is to find more integral inequalities of Hermite–Hadamard type for n-times differentiable and geometrically quasi-convex functions.

A Lemma

In order to obtain our main results, we need the following Lemma.

Lemma 1

(Wang and Shi 2016) For \(n\in {\mathbb {N}}\), let \(f:I\subseteq {\mathbb {R}}_+\rightarrow {\mathbb {R}}\) be a n-times differentiable function on \(I^\circ \) and \(a,b\in I\) with \(a< b\). If \(f^{(n)}\in L_1([a,b])\), then
$$\begin{aligned}&\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _a^{b}f(x){{\mathrm{d}}}x \\&\qquad = \frac{(-1)^{n-1}(\ln b-\ln a)}{n!}\int _0^1a^{(n+1)t}b^{(n+1)(1-t)}f^{(n)}\bigl (a^tb^{1-t}\bigr ) {{\mathrm{d}}}t. \end{aligned}$$

Remark 1

Under the conditions of Lemma 1, taking \(n=1\), we obtain
$$\begin{aligned} bf(b)-af(a)-\int _a^{b}f(x){{\mathrm{d}}}x = (\ln b-\ln a\bigr )\int _0^1a^{2t}b^{2(1-t)}f'\bigl (a^tb^{1-t}\bigr ) {{\mathrm{d}}}t, \end{aligned}$$
which can be found in Zhang et al. (2013).

Inequalities for geometrically quasi-convex functions

Now we start out to establish some new Hermite–Hadamard type inequalities for n-times differentiable and geometrically quasi-convex functions.

Theorem 5

For \(n\in {\mathbb {N}}\) , suppose that \(f:I\subseteq {\mathbb {R}}_+\rightarrow {\mathbb {R}}\) is a n-times differentiable function on \(I^\circ \) , that \(f^{(n)}\in L_1([a,b])\) , and that \(a,b\in I\) with \(a<b\) . If \(\bigl |f^{(n)}\bigr |^q\) is geometrically quasi-convex on [a,  b] for \(q\ge 1\) , then
$$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\\&\quad \le \frac{(\ln b-\ln a)}{n!}L\bigl (a^{n+1},b^{n+1}\bigr )\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}. \end{aligned}$$

Proof

By the geometric quasi-convexity of \(\bigl |f^{(n)}\bigr |^q\), Lemma 1, and Hölder’s inequality, one has
$$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\\&\quad\le \frac{\ln b-\ln a}{ n!}\int _0^1a^{(n+1)t}b^{(n+1)(1-t)}\Bigr |f^{(n)}\bigl (a^{t}b^{1-t}\bigr )\Bigr |{{\mathrm{d}}}t\\&\quad\le \frac{\ln b-\ln a}{ n!}\biggl [\int _0^1a^{(n+1)t}b^{(n+1)(1-t)}{{\mathrm{d}}}t\biggr ]^{1-1/q}\\&\quad \times \biggl \{\int _0^1a^{(n+1)t}b^{(n+1)(1-t)}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |^q,\bigr |f^{(n)}(b)\bigr |^q\bigr \} {{\mathrm{d}}}t\biggr \}^{1/q}\\&\quad= \frac{(\ln b-\ln a)L\bigl (a^{n+1}, b^{n+1}\bigr )}{ n!}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}. \end{aligned}$$
Theorem 5 is thus proved.\(\square \)

Corollary 1

Under the assumptions of Theorem 5, if \(q=1\), then
$$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\\&\quad \le \frac{\ln b-\ln a}{n!}L\bigl (a^{(n+1)},b^{(n+1)}\bigr )\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}. \end{aligned}$$

Theorem 6

For \(n\in {\mathbb {N}}\), suppose that \(f:I\subseteq {\mathbb {R}}_+\rightarrow {\mathbb {R}}\) is a n-times differentiable function on \(I^\circ \), that \(f^{(n)}\in L_1([a,b])\), and that \(a,b\in I\) with \(a<b\). If \(\bigl |f^{(n)}\bigr |^q\) is geometrically quasi-convex on [ab] for \(q>1\), then
$$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\le \frac{\ln b-\ln a}{n!}\\&\quad \times \Bigl [L\Bigl (a^\frac{q(n+1)-m}{q-1}, b^\frac{q(n+1)-r}{q-1}\Bigr )\Bigr ]^{1-1/q}\bigl [L\bigl (a^m, b^r\bigr )\bigr ]^{1/q} \sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \} \end{aligned}$$
for \(0\le m, r\le (n+1)q\).

Proof

From the geometric quasi-convexity of \(\bigl |f^{(n)}\bigr |^q\), Lemma 1, and Hölder’s inequality, we have
$$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\\&\le \frac{\ln b-\ln a}{ n!}\int _0^1a^{(n+1)t}b^{(n+1)(1-t)}\bigl |f^{(n)}\bigl (a^{t}b^{1-t}\bigr )\bigr |{{\mathrm{d}}}t\\&\le \frac{\ln b-\ln a}{ n!}\biggl [\int _0^1a^{[q(n+1)-m]t/(q-1)}b^{[q(n+1)-r](1-t)/(q-1)}{{\mathrm{d}}}t\biggr ]^{1-1/q}\\&\quad \times \biggl \{\int _0^1a^{mt}b^{r(1-t)}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |^q,\bigr |f^{(n)}(b)\bigr |^q\bigr \} {{\mathrm{d}}}t\biggr \}^{1/q}\\&= \frac{\ln b-\ln a}{n!}\Bigl [L\Bigr (a^\frac{q(n+1)-m}{q-1}, b^\frac{q(n+1)-r}{q-1}\Bigl )\Bigr ]^{1-1/q}\bigl [L\bigl (a^m, b^r\bigr )\bigr ]^{1/q}\\&\quad \times \sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}. \end{aligned}$$
The proof of Theorem 6 is complete. \(\square \)

Corollary 2

Under the conditions in Theorem 6,
  1. 1.
    if \(m=r=0\), then
    $$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\\&\quad \le \frac{\ln b-\ln a}{n!}\Bigl [L\Bigl (a^\frac{q(n+1)}{q-1}, b^\frac{q(n+1)}{q-1}\Bigr )\Bigr ]^{1-1/q}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}; \end{aligned}$$
     
  2. 2.
    if \(m=r=q(n+1)\), then
    $$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\\&\quad \le \frac{\ln b-\ln a}{ n!}\bigl [L\bigl (a^{q(n+1)}, b^{q(n+1)}\bigr )\bigr ]^{1/q}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}; \end{aligned}$$
     
  3. 3.
    if \(m=0\) and \(r=q(n+1)\), then
    $$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\le \frac{\ln b-\ln a}{n!}\\&\quad \times \Bigl [L\Bigl (a^\frac{q(n+1)}{q-1}, 1\Bigr )\Bigr ]^{1-1/q}\bigl [L\bigl (1, b^{q(n+1)}\bigr )\bigr ]^{1/q}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}; \end{aligned}$$
     
  4. 4.
    if \(m=n+1\) and \(r=q(n+1)\), then
    $$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\le \frac{\ln b-\ln a}{n!}\\&\quad \times \bigl [L\bigl (a^{n+1}, 1\bigr )\bigr ]^{1-1/q}\bigl [L\bigl (a^{n+1}, b^{q(n+1}\bigr )\bigr ]^{1/q}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}; \end{aligned}$$
     
  5. 5.
    if \(m=q(n+1)\) and \(r=0\), then
    $$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\le \frac{\ln b-\ln a}{n!}\nonumber \\&\quad \times \Bigl [L\Bigl (1, b^\frac{q(n+1)}{q-1}\Bigr )\Bigr ]^{1-1/q}\bigl [L\bigl (a^{q(n+1}, 1\bigr )\bigr ]^{1/q}\sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}; \end{aligned}$$
     
  6. 6.
    if \(m=q(n+1)\) and \(r=n+1\), then
    $$\begin{aligned}&\Biggl |\sum _{k=1}^{n}\frac{(-1)^{k-1}}{k!}\bigl [b^kf^{(k-1)}(b)-a^{k}f^{(k-1)}(a)\bigr ] -\int _{a}^{b}f(x){{\mathrm{d}}}x \Biggl |\le \frac{\ln b-\ln a}{n!}\\&\quad \times \bigl [L\bigl (1, b^{n+1}\bigr )\bigr ]^{1-1/q}\bigl [L\bigl (a^{q(n+1)}, b^{n+1}\bigr )\bigr ]^{1/q} \sup \bigl \{\bigr |f^{(n)}(a)\bigr |,\bigr |f^{(n)}(b)\bigr |\bigr \}. \end{aligned}$$
     

Conclusion

Our main results in this paper are those integral inequalities of Hermite–Hadamard type in Theorems 5 and 6 and Corollaries 1 and 2.

Declarations

Authors’ contributions

JZ, FQ, G-CX and Z-LP contributed equally to the manuscript. All authors read and approved the final manuscript.

Acknowledgements

This work was partially supported by the National Natural Science Foundation of China under Grant Nos. 61163034 and 61373067 and by the Inner Mongolia Autonomous Region Natural Science Foundation Project under Grant No. 2015MS0123, China. The authors appreciate anonymous referees for their valuable comments on and careful corrections to the original version of this paper.

Competing interests

The authors declare that they have no competing interests.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors’ Affiliations

(1)
College of Computer Science and Technology, Jilin University
(2)
College of Computer Science and Technology, Inner Mongolia University for Nationalities
(3)
Department of Mathematics, School of Science, Tianjin Polytechnic University
(4)
Institute of Mathematics, Henan Polytechnic University

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© Zhang et al. 2016