1. Introduction
In this paper, we denote a nonempty and open interval with .
We first review some definitions of various convex functions and list some Hermite–Hadamard-type integral inequalities.
It is general knowledge that a function
is said to be convex if
for all
and
. One can find a lot of classical conclusions for convex functions in monographs [
1,
2].
In [
3], Xi and his co-authors defined
-convex functions and
-convex functions and established some Hermite–Hadamard-type integral inequalities.
Definition 1 ([
3]).
For some and , a function is said to be -convex ifholds for all and . Definition 2 ([
3]).
For some and , a function is said to be -convex ifholds for all and . Definition 3 ([
4,
5]).
The function is said to be geometric-arithmetically convex, that is, GA-convex, on I ifholds for all and . In [
6], Shuang and her co-authors, including the second author of this paper, introduced the notion of the geometric-arithmetically
s-convex function and established some inequalities of the Hermite–Hadamard type for geometric-arithmetically
s-convex functions.
Definition 4 ([
6]).
Let and . A function is said to be geometric-arithmetically s-convex on I ifholds for all and . Remark 1. When , a geometric-arithmetically s-convex function becomes the GA-convex function defined in [4,5]. Remark 2. The integral estimates and applications of geometric-arithmetically convex functions have received renewed attention in recent years. A remarkable variety of refinements and generalizations have been found in, for example, [3,4,5,6]. In this paper, we will generalize the results of the above-mentioned literature and study the application problems. Let
be a convex function on
I. Then, the Hermite–Hadamard integral inequality reads that
One can find a lot of classical conclusions for the Hermite–Hadamard integral inequality in the monograph [
7].
Hermite–Hadamard-type integral inequalities are a very active research topic [
8]. We now recall some known results below.
Theorem 1 ([
9], Theorem 2.2).
Let be a differentiable mapping on , and let the points with . If is convex on , then Theorem 2 ([
10], Theorems 1 and 2).
Let be differentiable on , and let with . If is convex on for , thenand Theorem 3 ([
11]).
Let be m-convex and . If for , then Theorem 4 ([
12]).
Let be differentiable on , the numbers with , and . If is s-convex on for some fixed and , then Theorem 5 ([
13]).
Let be differentiable on , let with , and let . If is s-convex on for some fixed and , thenwhere . Theorem 6 ([
14]).
Let be differentiable on , let with , and let . If is s-convex on for some , then Motivated by the studies above, we will introduce the notions of “-geometric-arithmetically convex functions” and “-geometric-arithmetically convex functions”, and we will establish some new inequalities of the Hermite–Hadamard type for -geometric-arithmetically convex functions and for -geometric-arithmetically convex functions.
2. Definitions
We now introduce the notions of “-geometric-arithmetically convex functions” and “-geometric-arithmetically convex functions”.
Definition 5. For some and , a function is said to be -geometric-arithmetically convex, or simply speaking, -GA-convex ifholds for all and . Remark 3. By Definition 5, we can see that,
- 1.
If , then is an s-GA-convex function on I, see [6]; - 2.
If , then is a GA-convex function on I, see [4,5].
Definition 6. For some and , a function is said to be -geometric-arithmetically convex, or simply speaking, -GA-convex ifholds for all and . Remark 4. By Definition 6, we can see that:
- 1.
If , then is an -GA-convex function on ;
- 2.
If , then is an -GA-convex function on ;
- 3.
If , then is an -GA-convex function on .
It is obvious that:
- 1.
When , the function is strictly concave with respect to ;
- 2.
When , the function is convex with respect to .
Proposition 1. Let and . Then, the function for is -geometric-arithmetically convex with respect to .
Proof. We only need to verify the inequality
for all
and
.
For all and :
- 1.
When
, let
, then
and
; thus,
that is,
- 2.
The proof of Proposition 1 is complete. □
3. Lemmas
The following lemmas are necessary for us.
Lemma 1 ([
15]).
Let be differentiable on and let with . If , then for , we have Lemma 2. Let . Then,andwhere , anddenotes the classical Euler gamma function. Proof. By letting
for
and using the formulas
and
in [
16] (p. 259, 6.3.22), it is easy to show that
The proof of Lemma 2 is complete. □
4. Hermite–Hadamard-Type Integral Inequalities
In this section, we turn our attention to the establishment of integral inequalities of the Hermite–Hadamard type for -GA-convex and -GA-convex functions.
Theorem 7. For some and , let be a differentiable function on , let with and , and let and be decreasing on . If is -GA-convex on for , then the following conclusions are valid:
- 1.
When and , we havewhere and are defined byandfor ; - 2.
When and , we have
where , are defined in Lemma 2 anddenotes the classical beta function. Proof. For
and
, since
is decreasing on
, by Lemma 1 and the Hölder integral inequality, we have
Making use of the
-GA-convexity of
, we have
and
By using the above inequalities between (
3) and (
4) and then simplifying them, we obtain the required inequality (
1).
When
and
, by the inequalities between (
3) and (
4) and by Lemma 2, we have
The proof of Theorem 7 is complete. □
In Theorem 7, when taking
and
, we derive the same result as in [
6].
Corollary 1. Under the conditions of Theorem 7, with and , we have In Theorem 7, when setting , we deduce the following integral inequalities of the Hermite–Hadamard type for the GA-convex function.
Corollary 2. Under the conditions of Theorem 7, with , we have Corollary 3. Under the conditions of Theorem 7, with and , we obtain By making use of the same method as that in the proof of Theorem 7, we obtain the following integral inequalities for -GA-convex functions.
Theorem 8. For some fixed and , let with and , let be a differentiable function, let , and let be decreasing on . If is -GA-convex on for , then:
- 1.
When and , we have - 2.
When and , we have
where , , , and are defined respectively in Theorem 7 and Lemma 2.
Proof. Making use of the
-GA-convexity of
on
once again yields
and
We then substitute the two inequalities above into (
7) and simplify the result in the required inequality (
5).
Similarly, we can prove inequality (
6). The proof of Theorem 8 is complete. □
Corollary 4. In Theorem 8, if and , then Theorem 9. For some fixed and , let with and , let be a differentiable function, and let and be decreasing on . If is -GA-
convex on for , thenwhere is defined by (2) in Theorem 7. Proof. Since
is decreasing on
, by Lemma 1 and the Hölder integral inequality, we obtain
where
and
Note that in the above arguments, we used the fact that the function
is
-GA-convex on
. Applying the above equality and inequalities into (
9) and then simplifying them lead to the required inequality (
8). The proof of Theorem 9 is complete. □
Using the same method as that in the proof of Theorem 9, we obtain the following inequalities of -GA-convex functions.
Theorem 10. For some and , let be a differentiable function on , let with and , and let and be decreasing on . If is -GA-
convex on for , thenwhere is defined by (2) in Theorem 7. In Theorem 10, when
, the Hermite–Hadamard-type integral inequality is the same as the result in [
6].
Corollary 5 ([
6]).
Under the conditions of Theorem 10, if we take , then 5. Applications to Special Means
For two positive numbers
with
, define
and
These means are respectively called the arithmetic, harmonic, logarithmic, and generalized logarithmic means of
.
Theorem 11. Let with , let , and let .
Proof. In Corollary 1, let and . If and , the is decreasing on . By Proposition 1, we can derive the inequalities in Theorem 11. □
Corollary 6. Under the conditions of Theorem 11, with :
6. Conclusions
Integral inequalities are important for the prediction of upper and lower bounds in various aspects of applied sciences such as in Probability Theory, Functional Inequalities, and Information Theory.
In this paper, after recalling some convexities and the Hermite–Hadamard-type integral inequalities, we introduced the notions of -geometric-arithmetically convex functions and -geometric-arithmetically convex functions, established several integral inequalities of the Hermite–Hadamard type for -GA-convex and -GA-convex functions, and applied several results in the construction of several inequalities of special means.