Given two $n\times n$ positive definite matrices $A$ and $B$, the metric geometric mean introduced by Pusz and Woronowicz in 1975 is
$$ A\sharp B := A^{1/2}(A^{-1/2}BA^{-1/2})^{1/2}A^{1/2},$$
and the spectral geometric mean introduced by Fiedler and Pt\'ak in 1997 is
$$ A \natural B := (A^{-1}\sharp B)^{1/2}A(A^{-1}\sharp B)^{1/2}.$$
For $0\le t\le 1$, the $t$-metric geometric mean ($t$-geometric mean, for short) and $t$-spectral geometric mean ($t$-spectral mean, for short) of $A$ and $B$ are defined by
$$ A \sharp_t B & := &A^{1/2}(A^{-1/2}BA^{-1/2})^{t}A^{1/2},
A \natural_t B & := &(A^{-1}\sharp B)^{t}A(A^{-1}\sharp B)^{t}.$$
Some log majorization result involving $t$-metric geometric mean and $t$-spectral geometric mean are given. Some questions are asked.
谭天祐教授, 美国内华达大学雷诺分校(University of Nevada, Reno)数学与统计系终身教授、Seneca C. and Mary B. Weeks Chair in Mathematics、系主任。在加入 UNR 前, 他被选为奥本大学 Lloyd and Sandra Nix Endowed Professor (2012-2015) ,任系主任(2012-2018),任理科和数学学院评估与计划主任 (2000-2012)。他是奥本大学的荣誉退休教授。主要从事矩阵,多重线性代数,数值域和李群方面的研究。在国际学术期刊上发表主要学术论文 110 多篇和研究专著 Matrix Inequalities and their Extensions to Lie Groups, CRC/Taylor & Francis Group, 2018。他担任国际数学学术期刊《Linear and Multilinear Algebra》,《Electronic Linear Algebra》,《Special Matrices》的编委。他曾被邀请在国际数学会议上和各大学中作学术报告超過 250 次; 多次组织国际数学会议。在他指导下,十名博士生已经毕业。他担任 Pacific Journal of Mathematics 理事会成员 (自 2021 年起)、上海大学张量与矩阵理论国际研究中心科学委员会成员(自 2016 年起)。他担任美国《Mathematical Reviews》及德国《Zentralblatt Math》的评论员。