Abstract
According to the notion of the -mixed geominimal surface area of multiple convex bodies which were introduced by Ye et al., we define the concept of the -dual mixed geominimal surface area for multiple star bodies, and we establish several inequalities related to this concept.
MSC:52A20, 52A40.
Similar content being viewed by others
1 Introduction
Let denote the set of convex bodies (compact, convex subsets with nonempty interiors) in Euclidean space . For the set of convex bodies containing the origin in their interiors and the set of convex bodies whose centroids lie at the origin in , we write and , respectively. and , respectively, denote the set of star bodies (about the origin) and the set of star bodies whose centroids lie at the origin in . Let denote the set of that have a positive continuous curvate function. Let denote the unit sphere in and the n-dimensional volume of the body K. For the standard unit ball B in , its volume is written by .
The notion of -geominimal surface area was given by Lutwak in [1]. For , and , the -geominimal surface area, , of K is defined by
Here denotes -mixed volume of (see [1, 2]) and denotes the polar of L. For the case , is just the classical geominimal surface area which was introduced by Petty [3]. Some affine isoperimetric inequalities related to the classical and -geominimal surface areas can be found in [3–10]. Recently, the -geominimal surface area was successfully extended to any real p () by Ye in [11]. Especially, Ye et al. [12] studied the -mixed geominimal surface area for multiple convex bodies. For , they defined the -mixed geominimal surface areas for as
Here denotes the polar body of Q, and denotes a type of -mixed volume of , (see [12]).
Wang and Qi in [13] introduced the -dual geominimal surface area as follows: For , and , the -dual geominimal surface area, , of K is defined by
Here denotes the -dual mixed volume of (see Section 2).
Note that we extend L from an origin-symmetric convex body to in definition (1.1). Actually, we can prove that the results of [13] all are correct under this extension.
In this paper, we first define the -dual mixed geominimal surface area for multiple star bodies with the same idea in mind as [12].
Definition 1.1 For , , the -dual mixed geominimal surface areas, (), of , are defined by
Here denotes a type of -dual mixed volume of the star bodies , (see (2.5)).
Comparing the definitions (1.2) and (1.3), we easily obtain
When in (1.2), then
Further, we establish some inequalities for the -dual mixed geominimal surface area. Our results can be stated as follows.
Theorem 1.1 If , , , then
Equality holds in inequality (1.6) if and only if () all are dilates of each other. Equality holds in inequality (1.7) if and only if there exist constants (not all zero) such that, for all ,
In particular, if , then we have the following.
Corollary 1.1 If , , then
Equality holds in the second inequality of (1.8) if and only if () all are dilates of each other.
Using Corollary 1.1, we may get the following Blaschke-Santalö type inequality.
Corollary 1.2 If , , then
Equality holds in the second inequality of (1.9) if and only if () all are balls centered at the origin.
Theorem 1.2 If , , then
Theorem 1.3 If , , then
Equality holds in (1.10) and (1.11) if and only if each ().
2 Notations and background materials
2.1 Radial function and polar set
If K is a compact star-shaped (with respect to the origin) in , then its radial function, , is defined by (see [6, 14])
If is positive and continuous, K will be called a star body (with respect to the origin). Two star bodies K and L are said to be dilates (of one another) if is independent of .
If E is a nonempty subset in , the polar set, , of E is defined by (see [6, 14])
For and its polar body, the well-known Blaschke-Stantalö inequality can be stated (see [14]): If , then
with equality if and only if K is an ellipsoid centered at the origin.
2.2 Dual mixed volume
The dual mixed volume of star bodies was introduced by Lutwak (see [15]). For , the dual mixed volume, , of is given by
The classical Alexander-Fenchel inequality for the dual mixed volume (see [6, 14]) asserts that the integer m satisfies such that
with equality if and only if are all dilations of each other.
In particular, if , one has the Minkowski inequality
with equality if and only if are all dilations of each other.
2.3 -Dual mixed volume
Lutwak in [1] introduced the -dual mixed volume. For , , the -dual mixed volume, , of K and L is defined by
Associated with (2.4), for all , , and , we define
From (2.2) and (2.5), we easily get
If and in (2.5), then (2.4) and (2.5) yield
3 Results and proofs
In this section, we will prove Theorems 1.1-1.3 and Corollaries 1.1-1.2.
Proof of Theorem 1.1 We first prove inequality (1.7) is true.
Let be nonnegative bounded Borel functions on . By the Hölder inequality (see [16]), we have (see [14])
with equality if and only if there exist constants (not all zero) such that for all .
For , we let
In association with (2.5), we get
Combining with (1.3), (3.2), we get
i.e.,
This gives (1.7).
According to the equality condition of inequality (3.1), we see that equality holds in inequality (1.7) if and only if
for all , where ().
Now we complete the proof of (1.6). For , we let
In association with (2.5) and (3.1), we get
Similar to the proof of (1.7), combining with (1.2) and (3.3), we obtain
According to the equality condition of inequality (3.1), we see that equality holds in inequality (1.6) if and only if
for all , where (). This means that
for all , i.e., () all are dilates of each other. □
Proof of Corollary 1.1 Let in (1.6), and together with (1.4) and (1.5), we easily obtain
This gives (1.8).
From the equality condition of (1.6), we easily find that equality holds in the second inequality of (1.8) if and only if there exist constants (not all zero) such that, for all , . This means all () are dilates of each other. □
In order to prove Corollary 1.2, we give the following lemma.
Lemma 3.1 ([13])
If , , then
with equality if and only if K is a ball centered at the origin.
Proof of Corollary 1.2 Corollary 1.1, for K and , immediately yields
Combining with (3.5), (3.6), and (3.4), we obtain
i.e.,
This yields (1.9).
By the equality conditions of inequality (3.4) and the second inequality of (1.8), we know that equality holds in the second inequality of (1.9) if and only if all are balls centered at the origin. □
Proof of Theorem 1.2 From (1.3), it follows that, for any ,
Since , taking for , and using (2.6), (2.3), and (2.1), we get
This gives the proof of Theorem 1.2. □
Proof of Theorem 1.3 Using the Hölder inequality, (2.5), and (2.2), we get
that is,
According to the equality condition in the Hölder inequality, we know that equality holds in (3.7) if and only if there exist constants () such that for any , i.e., for each , and both are dilates.
From definition (1.3) and inequality (3.7), we have
i.e.,
This is just (1.11). Because of each in inequality (3.7), together with the equality condition of (3.7), we see that equality holds in (1.11) if and only if each .
In order to prove (1.10), (3.7) can be written
In the same way as (1.11), from definition (1.2) and (3.8), we get
From the equality condition in (1.11), we see that equality holds in (1.10) if and only if each . □
References
Lutwak E: The Brunn-Minkowski-Firey theory II: affine and geominimal surface areas. Adv. Math. 1996, 118: 244-294. 10.1006/aima.1996.0022
Lutwak E: The Brunn-Minkowski-Firey theory I: mixed volumes and the Minkowski problem. J. Differ. Geom. 1993, 38: 131-150.
Petty CM: Geominimal surface area. Geom. Dedic. 1974, 3: 77-97.
Petty CM: Affine isoperimetric problems. Annals of the New York Academy of Sciences 440. Discrete Geometry and Convexity 1985, 113-127.
Schneider R: Affine surface area and convex bodies of elliptic type. Period. Math. Hung. 2014. 10.1007/s10998-014-0050-3
Schneider R: Convex Bodies: The Brunn-Minkowski Theory. 2nd edition. Cambridge University Press, Cambridge; 2014.
Wang WD, Feng YB:A general -version of Petty’s affine projection inequality. Taiwan. J. Math. 2013,17(2):517-528.
Zhu BC, Li N, Zhou JZ:Isoperimetric inequalities for geominimal surface area. Glasg. Math. J. 2011, 53: 717-726. 10.1017/S0017089511000292
Zhu BC, Zhou JZ, Xu WX: Mixed geominimal surface area. J. Math. Anal. Appl. 2015, 422: 1247-1263. 10.1016/j.jmaa.2014.09.035
Zhu, BC, Zhou, JZ, Xu, WX: Affine isoperimetric inequalities for geominimal surface area. Springer Proceedings in Mathematics and Statistics (in press)
Ye, DP: On the L p -geominimal surface area and related inequalities (submitted). arXiv: 1308.4196
Ye, DP, Zhu, BC, Zhou, JZ: The mixed L p -geominimal surface areas for multiple convex bodies. arXiv: 1311.5180v1
Wang WD, Qi C:-Dual geominimal surface area. J. Inequal. Appl. 2011., 2011: Article ID 6
Gardner RJ: Geometric Tomography. 2nd edition. Cambridge University Press, Cambridge; 2006.
Lutwak E: Dual mixed volumes. Pac. J. Math. 1975, 58: 531-538. 10.2140/pjm.1975.58.531
Hardy GH, Littlewood JE, Pólya G: Inequalities. Cambridge University Press, Cambridge; 1959.
Acknowledgements
The authors would like to sincerely thank the referees for very valuable and helpful comments and suggestions which made the paper more accurate and readable. Research is supported in part by the Natural Science Foundation of China (Grant No. 11371224) and Foundation of Degree Dissertation of Master of China Three Gorges University (Grant No. 2014PY067).
Author information
Authors and Affiliations
Corresponding author
Additional information
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
All authors have equally contributed in designing a new algorithm and obtaining complexity results. All authors read and approved the final manuscript.
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0), which permits use, duplication, adaptation, distribution, and reproduction in any medium or format, as long as 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.
About this article
Cite this article
Li, Y., Wang, W. The -dual mixed geominimal surface area for multiple star bodies. J Inequal Appl 2014, 456 (2014). https://doi.org/10.1186/1029-242X-2014-456
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/1029-242X-2014-456