- Research
- Open access
- Published:
Some inequalities related to \(2\times 2\) block sector partial transpose matrices
Journal of Inequalities and Applications volume 2020, Article number: 90 (2020)
Abstract
In this article, two inequalities related to \(2\times 2\) block sector partial transpose matrices are proved, and we also present a unitarily invariant norm inequality for the Hua matrix which is sharper than an existing result.
1 Introduction
We denote by \(\mathbb{M}_{n}\) the set of \(n\times n\) complex matrices. \(\mathbb{M}_{n}(\mathbb{M}_{k})\) is the set of \(n\times n\) block matrices with each block in \(\mathbb{M}_{k}\). The \(n\times n\) identity matrix is denoted by \(I_{n}\). We use \(\|\cdot \|\) for an arbitrary unitarily invariant norm. A positive semidefinite matrix A will be expressed as \(A\geq 0\). Likewise, we write \(A>0\) to refer that A is a positive definite matrix. The singular values of A, denoted by \(s_{1}(A), s_{2}(A),\ldots, s_{n}(A)\), are the eigenvalues of the positive semidefinite matrix \(|A|=(A^{*}A)^{1/2}\), arranged in decreasing order and repeated according to multiplicity as \(s_{1}(A)\geq s_{2}(A)\geq \cdots \geq s_{n}(A)\). When A is Hermitian, we enumerate eigenvalues of A in nonincreasing order \(\sigma _{1}(A)\geq \sigma _{2}(A)\geq \cdots \geq \sigma _{n}(A)\). Recall that \(C\in \mathbb{M}_{m\times n}\) is (strictly) contractive if (\(I_{n}>C^{*}C\)) \({ I_{n} \geq C^{*}C}\). The geometric mean of two positive definite matrices \(A, B\in \mathbb{M}_{n}\), denoted by \(A\sharp B\), is the positive definite solution of the Riccati equation \(XB^{-1}X=A\) and has the explicit expression \(A\sharp B=A^{\frac{1}{2}}(A^{-\frac{1}{2}}BA^{-\frac{1}{2}})^{ \frac{1}{2}}A^{\frac{1}{2}}\). More details on the matrix geometric mean can be found in [2, Chap. 4].
The numerical range of \(A\in \mathbb{M}_{n}\) is defined by
For basic properties of numerical range, see [5]. Also, we define a sector on the complex plane
Actually, the class of matrices T with \(W(T)\subseteq S_{\alpha }\) and the class of T with positive definite real part (i.e. accretive matrices) are both called sector matrices. Sector matrices have been the subject of a number of recent papers [3, 8, 14].
A matrix \(H=(H_{ij})_{i,j=1}^{n}\in \mathbb{M}_{n}(\mathbb{M}_{k})\) is said to be positive partial transpose (i.e. PPT) if H is positive semidefinite and its partial transpose \(H^{\tau }=(H_{ji})_{j,i=1}^{n}\) is also positive semidefinite. Inspired by PPT, Kuai [6] defined a new conception called sectorial partial transpose (i.e. SPT). That is, if \(W(A)\subseteq S_{\alpha }\) for \(A=(A_{ij})_{i,j=1}^{n}\in \mathbb{M}_{n}(\mathbb{M}_{k})\), then \(W(A^{\tau })\subseteq S_{\alpha }\). Thus, it is natural to extend the results for PPT matrices to SPT matrices.
Hiroshima [4, Theorem 1] proved the following result.
Theorem 1.1
Letbe PPT. Then
As the application of Theorem 1.1, Lin and Hiroshima [10, Theorem 3.3] presented a relation between the norm of diagonal blocks of the Hua matrix, e.g., [12] and the norm of its off diagonal blocks.
Theorem 1.2
If the Hua matrix is given by
where\(A,B \in \mathbb{M}_{m\times n}\)are strictly contractive, then
for any unitarily invariant norm.
Actually, it was only recently observed that H is PPT; see [1].
Lin [7] obtained a singular value inequality for PPT matrices related to a linear map.
Theorem 1.3
Let\(A, B, X\in \mathbb{M}_{n}\). If
is PPT, then for the linear map\(\varPhi: C\rightarrow C+\operatorname{Tr}(C)I\),
In this paper, we extend Theorem 1.1 and Theorem 1.3 to SPT matrices and show a stronger inequality than (2).
2 Main results
We start with some lemmas. The first three lemmas are quite standard in matrix analysis.
Lemma 2.1
([13, p. 63])
If\(H\in \mathbb{M}_{n}\), then
Lemma 2.2
([11, Theorem 1])
Letbe positive semidefinite with\(A\in \mathbb{M}_{m}, B\in \mathbb{M}_{n}\). Then
Lemma 2.3
([2, p.106])
Let\(A, B\in \mathbb{M}_{n}\)be positive definite matrices. Then, for all\(X\in M_{n}\),
The next lemma is due to Zhang [14, Lemma 3.1].
Lemma 2.4
Let\(A\in \mathbb{M}_{n}\)have\(W(A)\subseteq S_{\alpha }\)for some\(\alpha \in [0, \frac{\pi }{2})\). Then
for any unitarily invariant norm.
The following result about geometric mean has been proved by Lin and Sun [9].
Lemma 2.5
Let\(A, B\in \mathbb{M}_{n}\)be matrices with positive semidefinite real part. Then
Now we are ready to present our results. The first theorem is an extension of Theorem 1.1.
Theorem 2.6
Let\(H_{11}, H_{12}, H_{21}, H_{22}\in \mathbb{M}_{n}\). Ifis SPT, then
for any unitarily invariant norm.
Proof
Since H is a sector partial transpose matrix, then we know that
is PPT.
So by (6) we have
□
Remark 2.7
When \(H_{12}=H_{21}^{*}\) and \(\alpha =0\), then H is PPT in Theorem 2.6. Thus, our result is Hiroshima’s inequality (1).
Next will give a stronger inequality than Theorem 1.2.
Theorem 2.8
Let the Hua matrix be given by
where\(A,B \in \mathbb{M}_{m\times n}\)are strictly contractive. Then
for any unitarily invariant norm.
Proof
Since H is PPT, then
are both positive semidefinite matrices.
Hence,
and
Clearly, by unitary similarity transformation,
is also positive semidefinite.
Therefore,
Thus,
In a similar way, we can prove
So
is PPT.
Therefore,
□
Remark 2.9
Obviously, our result is sharper than (2).
Finally, we present an extension of Theorem 1.3.
Theorem 2.10
Let\(A, B, X, Y\in \mathbb{M}_{n}\). Ifis SPT, then
where\(\varPhi: C\rightarrow C+\operatorname{Tr}(C)I\).
Proof
Since M is SPT, then
and
are both positive semidefinite matrices. Thus, ReM is PPT.
By Theorem 1.3, we have
Compute
□
Remark 2.11
References
Ando, T.: Positivity of operator-matrices of Hua-type. Banach J. Math. Anal. 2, 1–8 (2008)
Bhatia, R.: Positive Definite Matrices. Princeton University Press, Princeton (2007)
Drury, S.W., Lin, M.: Singular values inequalities for matrices with numerical ranges in a sector. Oper. Matrices 4, 1143–1148 (2014)
Hiroshima, T.: Majorization criterion for distillability of a bipartite quantum state. Phys. Rev. Lett. 91(5), 057902 (2003)
Horn, R.A., Johnson, C.R.: Topics in Matrix Analysis. Cambridge University Press, New York (1991)
Kuai, L.: An extension of the Fiedler–Markham determinant inequality. Linear Multilinear Algebra 66, 547–553 (2018)
Lin, M.: Inequalities related to 2 × 2 block PPT matrices. Oper. Matrices 94, 917–924 (2015)
Lin, M.: Some inequalities for sector matrices. Oper. Matrices 10, 915–921 (2016)
Lin, M., Sun, F.: A property of the geometric mean of accretive operator. Linear Multilinear Algebra 65, 433–437 (2017)
Lin, M., Wolkowicz, H.: Hiroshima’s theorem and matrix norm inequality. Acta Sci. Math. 81, 45–53 (2015)
Tao, Y.: More results on singular value inequalities of matrices. Linear Algebra Appl. 416, 724–729 (2006)
Xu, G., Xu, C., Zhang, F.: Contractive matrices of Hua type. Linear Multilinear Algebra 59, 159–172 (2011)
Zhan, X.: Matrix Theory. American Mathematical Society, Providence (2013)
Zhang, F.: A matrix decomposition and its applications. Linear Multilinear Algebra 63, 2033–2042 (2015)
Acknowledgements
Not applicable.
Availability of data and materials
Not applicable.
Funding
The work is supported by Hainan Provincial Natural Science Foundation for High-level Talents grant no. 2019RC171, the Ministry of Education of Hainan grant no. Hnky2019ZD-13, China Scholarship Council grant no. 201908460006, the Ministry of Education of Hainan grant no. Hnky2019ZD-13, the Provincial Key Laboratory, Hainan Normal University grant no. JSKX201904 and National Natural Science Foundation of China grant 11671105.
Author information
Authors and Affiliations
Contributions
All authors contributed almost the same amount of work to the manuscript. All authors read and approved the final manuscript.
Corresponding author
Ethics declarations
Competing interests
The authors declare that they have no competing interests.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, 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 licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Yang, J., Lu, L. & Chen, Z. Some inequalities related to \(2\times 2\) block sector partial transpose matrices. J Inequal Appl 2020, 90 (2020). https://doi.org/10.1186/s13660-020-02358-0
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/s13660-020-02358-0