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arXiv 1208.5603math.FAmath.CVmath.DG
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算子平均半群与广义Karcher方程

Semigroups of operator means and generalized Karcher equations

Miklós Pálfia

摘要:

本文考虑希尔伯特空间上正算子的平均。本文将矩阵论幂平均理论推广到Kubo-Ando意义下的任意算子平均。扩展的基础是依靠来自微分几何的思想。我们考虑广义Karcher方程的正算子,并表明,这样的方程承认唯一的正解,可以得到作为一个限制的一个参数家庭的运营商手段,称为诱导运营商手段。通过Kubo-Ando算子平均理论,这些平均是由将上半平面映射到自身的全纯函数半群所诱导的严格压缩的单参数族的唯一不动点。这些全纯函数半群被认为是与Schroeder的函数方程对应的Koenigs函数。柯尼希斯函数在此设置中为我们提供了对应于每个2变量算子均值的对数映射。2-变量平均值的半群表现为测地线,我们准确地分类的情况下,他们确实是测地线的仿射连通流形,从而提供的情况下,这些广义Karcher方程正是Karcher方程在几何意义上。这是通过研究出现的和乐群来实现的。这些广义Karcher方程的唯一解被称为lambda扩展,并具有许多从诱导算子本身继承的理想性质。

英文摘要:

In this article we consider means of positive operators on a Hilbert space. We extend the theory of matrix power means to arbitrary operator means in the sense of Kubo-Ando. The basis of the extension is relying on ideas coming from differential geometry. We consider generalized Karcher equations for positive operators and show that such equations admit unique positive solutions that can be obtained as a limit of one-parameter families of operator means called induced operator means. These means are themselves unique fixed points of one parameter families of strict contractions induced, through Kubo-Ando theory of operator means, by semigroups of holomorphic functions mapping the upper half-plane into itself. These semigroups of holomorphic functions are considered with Koenigs function corresponding to Schroeder's functional equation. Koenigs function in this setting provides us with a logarithm map corresponding to every 2-variable operator mean. The semigroups of 2-variable means behave as geodesics and we exactly classify the cases when they are indeed geodesics of affinely connected manifolds, thereby providing the cases when these generalized Karcher equations are exactly Karcher equations in the geometric sense. This is achieved by studying the arising holonomy groups. The unique solutions of these generalized Karcher equations are called lambda extensions and have numerous desirable properties which are inherited from the induced operator means themselves.

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