We establish some new properties of spectral geometric mean. In particular, we prove a log majorization relation between $left(B^{ts/2}A^{(1-t)s}B^{ts/2} right)^{1/s}$ and the $t$-spectral mean $A atural_t B :=(A^{-1}sharp B)^{t}A(A^{-1}sharp B)^{t}$
of two positive semidefinite matrices $A$ and $B$, where $Asharp B$ is the geometric mean, and the $t$-spectral mean is the dominant one. The limit involving $t$-spectral mean is also studied. We then extend all the results in the context of symmetric spaces of negative curvature.
In this paper, we give a simple formula for sectional curvatures on the general linear group, which is also valid for many other matrix groups. Similar formula is given for a reductive Lie group. We also discuss the relation between commuting matrices and zero sectional curvature.
In this paper, we study the metric geometric mean introduced by Pusz and Woronowicz and the spectral geometric mean introduced by Fiedler and Ptak, originally for positive definite matrices. The relation between $t$-metric geometric mean and $t$-spec
tral geometric mean is established via log majorization. The result is then extended in the context of symmetric space associated with a noncompact semisimple Lie group. For any Hermitian matrices $X$ and $Y$, Sos matrix exponential formula asserts that there are unitary matrices $U$ and $V$ such that $$e^{X/2}e^Ye^{X/2} = e^{UXU^*+VYV^*}.$$ In other words, the Hermitian matrix $log (e^{X/2}e^Ye^{X/2})$ lies in the sum of the unitary orbits of $X$ and $Y$. Sos result is also extended to a formula for adjoint orbits associated with a noncompact semisimple Lie group.
We give some statements that are equivalent to the existence of group inverses of Peirce corner matrices of a $2 times 2$ block matrix and its generalized Schur complements. As applications, several new results for the Drazin inverses of the generali
zed Schur complements and the $2 times 2$ block matrix are obtained and some of them generalize several results in the literature.
Denote by $P_n$ the set of $ntimes n$ positive definite matrices. Let $D = D_1oplus dots oplus D_k$, where $D_1in P_{n_1}, dots, D_k in P_{n_k}$ with $n_1+cdots + n_k=n$. Partition $Cin P_n$ according to $(n_1, dots, n_k)$ so that $Diag C = C_1oplus
dots oplus C_k$. We prove the following weak log majorization result: begin{equation*} lambda (C^{-1}_1D_1oplus cdots oplus C^{-1}_kD_k)prec_{w ,log} lambda(C^{-1}D), end{equation*} where $lambda(A)$ denotes the vector of eigenvalues of $Ain Cnn$. The inequality does not hold if one replaces the vectors of eigenvalues by the vectors of singular values, i.e., begin{equation*} s(C^{-1}_1D_1oplus cdots oplus C^{-1}_kD_k)prec_{w ,log} s(C^{-1}D) end{equation*} is not true. As an application, we provide a generalization of a determinantal inequality of Matic cite[Theorem 1.1]{M}. In addition, we obtain a weak majorization result which is complementary to a determinantal inequality of Choi cite[Theorem 2]{C} and give a weak log majorization open question.
Let ngeq3 and J_{n}:=circ(J_{1},J_{2},...,J_{n}) and j_{n}:=circ(j_{0},j_{1},...,j_{n-1}) be the ntimesn circulant matrices, associated with the nth Jacobsthal number J_{n} and the nth Jacobsthal-Lucas number j_{n}, respectively. The determinants of
J_{n} and j_{n} are obtained in terms of the Jacobsthal and Jacobsthal-Lucas numbers. These imply that J_{n} and j_{n} are invertible. We also derive the inverses of J_{n} and j_{n}.
