arXiv subjects
Publications and source records attributed to Mohammad Sal Moslehian.
In celebration of the distinguished achievements of Professor Tsuyoshi Ando in matrix analysis and operator theory, we conducted an interview with him via email. This paper presents Professor Ando's responses to several questions we gave him regarding his education and life as a mathematician.
We present several matrix and operator inequalities of Hermite-Hadamard type. We first establish a majorization version for monotone convex functions on matrices. We then utilize the Mond-Pecaric method to get an operator version for convex functions. We also present some applications. Finally we obtain an Hermite-Hadamard inequality for operator convex functions, positive linear maps and operators acting on Hilbert spaces.
We introduce the non-commutative $f$-divergence functional $Θ(\widetilde{A},\widetilde{B}):=\int_TB_t^{\frac{1}{2}}f\left(B_t^{-\frac{1}{2}} A_tB_t^{-\frac{1}{2}}\right)B_t^{\frac{1}{2}}dμ(t)$ for an operator convex function $f$, where $\widetilde{A}=(A_t)_{t\in T}$ and $\widetilde{B}=(B_t)_{t\in T}$ are continuous fields of Hilbert space operators and study its properties. We establish some relations between the perspective of an operator convex function $f$ and the non-commutative $f$-divergence functional. In particular, an operator extension of Csiszár's result regarding $f$-divergence functional is presented. As some applications, we establish a refinement of the Choi--Davis--Jensen operator inequality, obtain some unitarily invariant norm inequalities and give some results related to the Kullback--Leibler distance.
In this paper we introduce the notion of weak 2-positivity and present some examples. We establish some operator Cauchy--Schwarz inequalities involving the geometric mean and give some applications. In particular, we present some operator versions of Hua's inequality by using the Choi--Davis--Jensen inequality.
In this paper, we establish a link between the Hyers-Ulam stability and the Moore--Penrose inverse, that is, a closed operator has the Hyers-Ulam stability if and only if it has a bounded Moore-Penrose inverse. Meanwhile, the stability constant can be determined in terms of the Moore-Penrose inverse. Based on this result, some conditions for the perturbed operators having the Hyers--Ulam stability are obtained and the Hyers-Ulam stability constant is expressed explicitly in the case of closed operators. In the case of the bounded linear operators we obtain some characterizations for the Hyers-Ulam stability constants to be continuous. As an application, we give a characterization for the Hyers-Ulam stability constants of the semi-Fredholm operators to be continuous.
We extend the celebrated Löwner--Heinz inequality by showing that if $A, B$ are Hilbert space operators such that $A > B \geq 0$, then A^r - B^r \geq ||A||^r-(||A||- \frac{1}{||(A-B)^{-1}||})^r > 0 for each $0 < r \leq 1$. As an application we prove that \log A - \log B \geq \log||A||- \log(||A||-\frac{1}{||(A-B)^{-1}||})>0.
In this paper we introduce a notion of Morita equivalence for Hilbert C*-modules in terms of the Morita equivalence of the algebras of compact operators on Hilbert C*-modules. We investigate some properties of the new version of Morita equivalence and obtain some results. We then applied our results to study the continuous actions of locally compact groups on full Hilbert C*-modules. We present an extension of Green's theorem in the context of Hilbert C*-modules as well.
There are several inequalities in the literature carrying the name of Ky Fan. We survey these well-known Ky Fan inequalities and some other significant inequalities generalized by Ky Fan and review some of their recent developments.
For a probability measure $μ$ and for square integrable fields $(\mathscr{A}_t)$ and $(\mathscr{B}_t)$ ($t\inΩ$) of commuting normal operators we prove Landau type inequality \llu\int_Ω\mathscr{A}_tX\mathscr{B}_tdμ(t)- \int_Ω\mathscr{A}_t\,dμ(t)X \int_Ω\mathscr{B}_t\,dμ(t) \rru \le \llu \sqrt{\,\int_Ω|\mathscr{A}_t|^2\dt-|\int_Ω\mathscr{A}_t\dt|^2}X \sqrt{\,\int_Ω|\mathscr{B}_t|^2 \dt-|\int_Ω\mathscr{B}_t\dt|^2} \rru for all $X\in\mathcalb{B}(\mathcal{H})$ and for all unitarily invariant norms $\lluo\cdot\rruo$. For Schatten $p$-norms similar inequalities are given for arbitrary double square integrable fields. Also, for all bounded self-adjoint fields satisfying $C\le\mathscr{A}_t\le D$ and $E\le\mathscr{B}_t\le F$ for all $t\inΩ$ and some bounded self-adjoint operators $C,D,E$ and $F$, then for all $X\in\ccu$ we prove Grüss type inequality \llu\int_Ω\mathscr{A}_tX\mathscr{B}_t \dt- \int_Ω\mathscr{A}_t\,dμ(t)X \int_Ω\mathscr{B}_t\,dμ(t) \rru\leq \frac{\|D-C\|\cdot\|F-E\|}4\cdot\lluo X\rruo. More general results for arbitrary bounded fields are also given.
We prove some refinements of an inequality due to X. Zhan in an arbitrary complex Hilbert space by using some results on the Heinz inequality. We present several related inequalities as well as new variants of the Corach--Porta--Recht inequality. We also characterize the class of operators satisfying $\left\Vert SXS^{-1}+S^{-1}XS+kX\right\Vert \geq (k+2)\left\Vert X\right\Vert$ under certain conditions.
We establish a generalization of the Dunkl--Williams inequality and its inverse in the framework of Hilbert $C^*$-modules and characterize the equality case. As applications, we get some new results and some known results due to Pečarić and Rajić [Linear Algebra Appl. 425 (2007), no. 1, 16--25].
We survey several significant results on the Bohr inequality and presented its generalizations in some new approaches. These are some Bohr type inequalities of Hilbert space operators related to the matrix order and the Jensen inequality. An eigenvalue extension of Bohr's inequality is discussed as well.
Let $\mathcal{C}_p$ be the Schatten $p$-class for $p>0$. Generalizations of the parallelogram law for the Schatten 2-norms have been given in the following form: If $\mathbf{A}=\{A_1,A_2,...,A_n\}$ and $\mathbf{B}=\{B_1,B_2,...,B_n\}$ are two sets of operators in $\mathcal{C}_2$, then $$\sum_{i,j=1}^n\|A_i-A_j\|_2^2 + \sum_{i,j=1}^n\|B_i-B_j\|_2^2 = 2\sum_{i,j=1}^n\|A_i-B_j\|_2^2 - 2\Norm{\sum_{i=1}^n(A_i-B_i)}_2^2.$$ In this paper, we give generalizations of this as pairs of inequalities for Schatten $p$-norms, which hold for certain values of $p$ and reduce to the equality above for $p=2$. Moreover, we present some related inequalities for three sets of operators.
We present a weak majorization inequality and apply it to prove eigenvalue and unitarily invariant norm extensions of a version of the Bohr's inequality due to Vasić and Kečkić.
We establish a general operator parallelogram law concerning a characterization of inner product spaces, get an operator extension of Bohr's inequality and present several norm inequalities. More precisely, let ${\mathfrak A}$ be a $C^*$-algebra, $T$ be a locally compact Hausdorff space equipped with a Radon measure $μ$ and let $(A_t)_{t\in T}$ be a continuous field of operators in ${\mathfrak A}$ such that the function $t \mapsto A_t$ is norm continuous on $T$ and the function $t \mapsto \|A_t\|$ is integrable. If $α: T \times T \to \mathbb{C}$ is a measurable function such that $\bar{α(t,s)}α(s,t)=1$ for all $t, s \in T$, then we show that \begin{align*} \int_T\int_T&\left|α(t,s) A_t-α(s,t) A_s\right|^2dμ(t)dμ(s)+\int_T\int_T\left|α(t,s) B_t-α(s,t) B_s\right|^2dμ(t)dμ(s) \nonumber &= 2\int_T\int_T\left|α(t,s) A_t-α(s,t) B_s\right|^2dμ(t)dμ(s) - 2\left|\int_T(A_t-B_t)dμ(t)\right|^2\,. \end{align*}
We establish several operator versions of the classical Aczel inequality. One of operator versions deals with the weighted operator geometric mean and another is related to the positive sesquilinear forms. Some applications including the unital positive linear maps on $C^*$-algebras and the unitarily invariant norms on matrices are presented.
In this paper we present a new criterion on characterization of real inner product spaces. We conclude that a real normed space $(X, \|...\|)$ is an inner product space if $$\sum_{ε_i \in \{-1,1\}} \|x_1 + \sum_{i=2}^kε_ix_i\|^2=\sum_{ε_i \in \{-1,1\}} (\|x_1\| + \sum_{i=2}^kε_i\|x_i\|)^2,$$ for some positive integer $k\geq 2$ and all $x_1, ..., x_k \in X$. Conversely, if $(X, \|...\|)$ is an inner product space, then the equality above holds for all $k\geq 2$ and all $x_1, ..., x_k \in X$.
Suppose that $\mathcal{X}$ is a sequentially complete Hausdorff locally convex space over a scalar field $\mathbb{K}$, $V$ is a bounded subset of $\mathcal{X}$, $(a_n)_{n\ge 0}$ is a sequence in $\mathbb{K}\setminus\{0\}$ with the property\ $\ds\liminf_{n\to\infty} |a_n|>1$ and $(b_n)_{n\ge 0}$ is a sequence in $\mathcal{X}$. We show that for every sequence $(x_n)_{n\ge 0}$ in $\mathcal{X}$ satisfying \begin{eqnarray*} x_{n+1}-a_nx_n-b_n\in V\q(n\geq 0) \end{eqnarray*} there exists a unique sequence $(y_n)_{n\ge 0}$ satisfying the recurrence $y_{n+1}=a_ny_n+b_n\,\,(n\geq 0)$ and for every $q$ with $1<q<\ds\liminf_{n\to\infty} |a_n|$, there exists $n_0\in \mathbb{N}$ such that \begin{eqnarray*} x_n-y_n\in \ds\f{1}{q-1}\ov{conv(V^b)}\q (n\geq n_0). \end{eqnarray*}