1 Introduction and main results
Let
denote the set of convex bodies (compact, convex subsets with nonempty interiors) in Euclidean space ℝ
n
. For the set of convex bodies containing the origin in their interiors and the set of origin-symmetric convex bodies in ℝ
n
, we write
and
, respectively. Let
denote the set of star bodies (about the origin) in R
n
. Let Sn-1denote the unit sphere in ℝ
n
; denote by V (K) the n-dimensional volume of body K; for the standard unit ball B in ℝ
n
, denote ω
n
= V (B).
denote the set of convex bodies (compact, convex subsets with nonempty interiors) in Euclidean space ℝ
n
. For the set of convex bodies containing the origin in their interiors and the set of origin-symmetric convex bodies in ℝ
n
, we write
and
, respectively. Let
denote the set of star bodies (about the origin) in R
n
. Let Sn-1denote the unit sphere in ℝ
n
; denote by V (K) the n-dimensional volume of body K; for the standard unit ball B in ℝ
n
, denote ω
n
= V (B).The notion of geominimal surface area was given by Petty [1]. For
, the geominimal surface area, G(K), of K is defined by
, the geominimal surface area, G(K), of K is defined by
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According to the L
p
-mixed volume, Lutwak [3] introduced the notion of L
p
-geominimal surface area. For
, p ≥ 1, the L
p
-geominimal surface area, G
p
(K), of K is defined by
, p ≥ 1, the L
p
-geominimal surface area, G
p
(K), of K is defined by
(1.1)
Here V
p
(M, N) denotes the L
p
-mixed volume of
[3, 4]. Obviously, if p = 1, G
p
(K) is just the geominimal surface area G(K). Further, Lutwak [3] proved the following result for the L
p
-geominimal surface area.
[3, 4]. Obviously, if p = 1, G
p
(K) is just the geominimal surface area G(K). Further, Lutwak [3] proved the following result for the L
p
-geominimal surface area.Theorem 1.A. If
, p ≥ 1, then
, p ≥ 1, then
(1.2)
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with equality if and only if K is an ellipsoid.
Lutwak [3] also defined the L
p
-geominimal area ratio as follows: For
, the L
p
-geominimal area ratio of K is defined by
, the L
p
-geominimal area ratio of K is defined by
(1.3)
Lutwak [3] proved (1.3) is monotone nondecreasing in p, namely
Theorem 1.B. If
, 1 ≤ p < q, then
, 1 ≤ p < q, then
with equality if and only if K and T
p
K are dilates.
Above, the definition of L
p
-geominimal surface area is based on the L
p
-mixed volume. In this paper, associated with the L
p
-dual mixed volume, we give the notion of L
p
-dual geominimal surface area as follows: For
, and p ≥ 1, the L
p
-dual geominimal surface area,
, of K is defined by
, and p ≥ 1, the L
p
-dual geominimal surface area,
, of K is defined by
(1.4)
For the L
p
-dual geominimal surface area, we proved the following dual forms of Theorems 1.A and 1.B, respectively.
Theorem 1.1. If
, p ≥ 1, then
, p ≥ 1, then
(1.5)
with equality if and only if K is an ellipsoid centered at the origin.
Theorem 1.2. If
, 1 ≤ p < q, then
, 1 ≤ p < q, then
(1.6)
with equality if and only if
.
.Here
may be called the L
p
-dual geominimal surface area ratio of
.
.Further, we establish Blaschke-Santaló type inequality for the L
p
-dual geominimal surface area as follows:
Theorem 1.3. If
, n ≥ p ≥ 1, then
, n ≥ p ≥ 1, then
(1.7)
with equality if and only if K is an ellipsoid.
Finally, we give the following Brunn-Minkowski type inequality for the L
p
-dual geominimal surface area.
Theorem 1.4. If
, p ≥ 1 and λ, μ ≥ 0 (not both zero), then
, p ≥ 1 and λ, μ ≥ 0 (not both zero), then
(1.8)
with equality if and only if K and L are dilates.
Here λ ⋆ K +
-p
μ ⋆ L denotes the L
p
-harmonic radial combination of K and L.
The proofs of Theorems 1.1-1.3 are completed in Section 3 of this paper. In Section 4, we will give proof of Theorem 1.4.
2 Preliminaries
2.1 Support function, radial function and polar of convex bodies
where x·y denotes the standard inner product of x and y.
If K is a compact star-shaped (about the origin) in R
n
, then its radial function, ρ
K
= ρ (K,·): R
n
\{0} → [0, ∞), is defined by [5, 6]
If ρ
K
is continuous and positive, then K will be called a star body. Two star bodies K, L are said to be dilates (of one another) if ρ
K
(u)/ρ
L
(u) is independent of u ∈ Sn-1.
For
, if ϕ ∈ GL(n), then by (2.1) we know that
, if ϕ ∈ GL(n), then by (2.1) we know that
(2.2)
Here GL(n) denotes the group of general (nonsingular) linear transformations and ϕ
-τ
denotes the reverse of transpose (transpose of reverse) of ϕ.
For
and its polar body, the well-known Blaschke-Santaló inequality can be stated that [5]:
and its polar body, the well-known Blaschke-Santaló inequality can be stated that [5]:Theorem 2.A. If
, then
, then
(2.3)
with equality if and only if K is an ellipsoid.
2.2 L p -Mixed volume
where "·" in ε·L denotes the Firey scalar multiplication.
Theorem 2.B. If
and p ≥ 1 then
and p ≥ 1 then
(2.4)
with equality for p > 1 if and only if K and L are dilates, for p = 1 if and only if K and L are homothetic.
2.3 L p -Dual mixed volume
For
, p ≥ 1 and λ, μ ≥ 0 (not both zero), the L
p
harmonic-radial combination,
of K and L is defined by [3]
, p ≥ 1 and λ, μ ≥ 0 (not both zero), the L
p
harmonic-radial combination,
of K and L is defined by [3]
(2.5)
From (2.5), for ϕ ∈ GL(n), we have that
(2.6)
Associated with the L
p
-harmonic radial combination of star bodies, Lutwak [3] introduced the notion of L
p
-dual mixed volume as follows: For
, p ≥ 1 and ε > 0, the L
p
-dual mixed volume,
of the K and L is defined by [3]
, p ≥ 1 and ε > 0, the L
p
-dual mixed volume,
of the K and L is defined by [3]
(2.7)
The definition above and Hospital's role give the following integral representation of the L
p
-dual mixed volume [3]:
(2.8)
where the integration is with respect to spherical Lebesgue measure S on Sn- 1.
From the formula (2.8), we get
(2.9)
Theorem 2.C. Let
, p ≥ 1, then
, p ≥ 1, then
(2.10)
with equality if and only if K and L are dilates.
2.4 L p -Curvature image
Equation (2.11) is also called Radon-Nikodym derivative, it turns out that the measure S
p
(K, ·) is absolutely continuous with respect to surface area measure S(K, ·).
A convex body
is said to have an L
p
-curvature function [3]f
p
(K, ·): Sn-1→ ℝ, if its L
p
-surface area measure S
p
(K, ·) is absolutely continuous with respect to spherical Lebesgue measure S, and
is said to have an L
p
-curvature function [3]f
p
(K, ·): Sn-1→ ℝ, if its L
p
-surface area measure S
p
(K, ·) is absolutely continuous with respect to spherical Lebesgue measure S, and
Let
, denote set of all bodies in
,
, respectively, that have a positive continuous curvature function.
, denote set of all bodies in
,
, respectively, that have a positive continuous curvature function.Lutwak [3] showed the notion of L
p
-curvature image as follows: For each
and real p ≥ 1, define
, the L
p
-curvature image of K, by
and real p ≥ 1, define
, the L
p
-curvature image of K, by
3 L p -Dual geominimal surface area
In this section, we research the L
p
-dual geominimal surface area. First, we give a property of the L
p
-dual geominimal surface area under the general linear transformation. Next, we will complete proofs of Theorems 1.1-1.3.
For the L
p
-geominimal surface area, Lutwak [3] proved the following a property under the special linear transformation.
Theorem 3.A. For
, p ≥ 1, if ϕ ∈ SL(n), then
, p ≥ 1, if ϕ ∈ SL(n), then
(3.1)
Here SL(n) denotes the group of special linear transformations.
Similar to Theorem 3.A, we get the following result of general linear transformation for the L
p
-dual geominimal surface area:
Theorem 3.1. For
, p ≥ 1, if ϕ ∈ GL(n), then
, p ≥ 1, if ϕ ∈ GL(n), then
(3.2)
Lemma 3.1. If
and p ≥ 1, then for ϕ ∈ GL(n),
and p ≥ 1, then for ϕ ∈ GL(n),
(3.3)
Proof. From (2.6), (2.7) and notice the fact V (ϕ K) = |detϕ|V (K), we have
□
Proof of Theorem 3.1. From (1.4), (3.3) and (2.2), we have
This immediately yields (3.2). □
we may extend Theorem 3.A as follows:
Theorem 3.2. For
, p ≥ 1, if ϕ ∈ GL(n), then
, p ≥ 1, if ϕ ∈ GL(n), then
(3.4)
Obviously, (3.2) is dual form of (3.4). In particular, if ϕ ∈ SL(n), then (3.4) is just (3.1).
Now we prove Theorems 1.1-1.3.
Proof of Theorem 1.1. From (2.10) and Blaschke-Santaló inequality (2.3), we have that
Hence, using definition (1.4), we know
this yield inequality (1.5). According to the equality conditions of (2.3) and (2.10), we see that equality holds in (1.5) if and only if K and
are dilates and Q is an ellipsoid, i.e. K is an ellipsoid centered at the origin. □
are dilates and Q is an ellipsoid, i.e. K is an ellipsoid centered at the origin. □Compare to inequalities (1.2) and (1.5), we easily get that
Corollary 3.1. For
, p ≥ 1, then for n > p,
, p ≥ 1, then for n > p,
with equality if and only if K is an ellipsoid centered at the origin.
Proof of Theorem 1.2. Using the Hölder inequality, (2.8) and (2.9), we obtain
that is
(3.5)
According to equality condition in the Hölder inequality, we know that equality holds in (3.5) if and only if K and Q are dilates.
From definition (1.4) of
, we obtain
, we obtain
(3.6)
This gives inequality (1.6).
Because of
in inequality (3.6), this together with equality condition of (3.5), we see that equality holds in (1.6) if and only if
. □
in inequality (3.6), this together with equality condition of (3.5), we see that equality holds in (1.6) if and only if
. □Proof of Theorem 1.3. From definition (1.4), it follows that for
,
,
Since
, taking K for Q, and using (2.9), we can get
, taking K for Q, and using (2.9), we can get
(3.7)
Similarly,
(3.8)
From (3.7) and (3.8), we get
Hence, for n ≥ p using (2.3), we obtain
According to the equality condition of (2.3), we see that equality holds in (1.7) if and only if K is an ellipsoid. □
Associated with the L
p
-curvature image of convex bodies, we may give a result more better than inequality (1.5) of Theorem 1.1.
Theorem 3.3. If
, p ≥ 1, then
, p ≥ 1, then
(3.9)
with equality if and only if
.
.
Proof of Theorem 3.3. From (1.4), (3.10) and (2.4), we have that
This yields (3.9). According to the equality condition in inequality (2.4), we see that equality holds in inequality (3.9) if and only if K and Q* are dilates. Since
, equality holds in inequality (3.9) if and only if
. □
, equality holds in inequality (3.9) if and only if
. □
with equality if and only if K is an ellipsoid.
From (3.9) and (3.11), we easily get that if
and p ≥ 1, then
and p ≥ 1, then
(3.12)
with equality if and only if K is an ellipsoid.
Inequality (3.12) just is inequality (1.5) for the L
p
-curvature image.
In addition, by (1.2) and (3.9), we also have that
Corollary 3.2. If
, p ≥ 1, then
, p ≥ 1, then
with equality if and only if K is an ellipsoid.
4 Brunn-Minkowski type inequalities
In this section, we first prove Theorem 1.4. Next, associated with the L
p
-harmonic radial combination of star bodies, we give another Brunn-Minkowski type inequality for the L
p
-dual geominimal surface area.
Lemma 4.1. If
, p ≥ 1 and λ, μ ≥ 0 (not both zero) then for any
,
, p ≥ 1 and λ, μ ≥ 0 (not both zero) then for any
,
(4.1)
with equality if and only if K and L are dilates.
Proof. Since -(n + p)/p < 0, thus by (2.5), (2.8) and Minkowski's integral inequality (see [14]), we have for any
,
,
According to the equality condition of Minkowski's integral inequality, we see that equality holds in (4.1) if and only if K and L are dilates. □
Proof of Theorem 1.4. From definition (1.4) and inequality (4.1), we obtain
This yields inequality (1.8).
By the equality condition of (4.1) we know that equality holds in (1.8) if and only if K and L are dilates. □
The notion of L
p
-radial combination can be introduced as follows: For
, p ≥ 1 and λ, μ ≥ 0 (not both zero), the L
p
-radial combination,
, of K and L is defined by [15]
, p ≥ 1 and λ, μ ≥ 0 (not both zero), the L
p
-radial combination,
, of K and L is defined by [15]
(4.2)
Under the definition (4.2) of L
p
-radial combination, we also obtain the following Brunn-Minkowski type inequality for the L
p
-dual geominimal surface area.
Theorem 4.1. If
, p ≥ 1 and λ, μ ≥ 0 (not both zero), then
, p ≥ 1 and λ, μ ≥ 0 (not both zero), then
(4.3)
with equality if and only if K and L are dilates.
Proof. From definitions (1.4), (4.2) and formula (2.8), we have
Thus
The equality holds if and only if
are dilates with K and L, respectively. This mean that equality holds in (4.3) if and only if K and L are dilates. □
are dilates with K and L, respectively. This mean that equality holds in (4.3) if and only if K and L are dilates. □Acknowledgements
We wish to thank the referees for this paper. Research is supported in part by the Natural Science Foundation of China (Grant No. 10671117) and Science Foundation of China Three Gorges University.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
In the article, WW complete the proof of Theorems 1.1-1.3, 3.1-3.3, QC give the proof of Theorems 1.4 and 4.1. WW carry out the writing of whole manuscript. All authors read and approved the final manuscript.