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arXiv 1202.5071math.DS
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f-不变熵的一个子群公式

A subgroup formula for f-invariant entropy

Brandon Seward

摘要:

我们研究了一个测量熵的非线性产生的自由群作用称为f-不变熵。f-不变熵是由路易斯·鲍文提出的,本质上是他的测度熵理论在sofic群作用下的一个特例。本文将群生成的自由群作用的f-不变熵与子群的限制作用的f-不变熵联系起来。我们证明了这些熵的比值等于子群的指数。这推广了一个众所周知的公式的Kolmogorov-Sinai熵的顺从组行动。然后,我们将f-不变熵的定义推广到了虚自由群的作用。我们还得到了一个数值虚测度共轭不变量的作用下生成的虚拟自由群。

英文摘要:

We study a measure entropy for finitely generated free group actions called f-invariant entropy. The f-invariant entropy was developed by Lewis Bowen and is essentially a special case of his measure entropy theory for actions of sofic groups. In this paper we relate the f-invariant entropy of a finitely generated free group action to the f-invariant entropy of the restricted action of a subgroup. We show that the ratio of these entropies equals the index of the subgroup. This generalizes a well known formula for the Kolmogorov--Sinai entropy of amenable group actions. We then extend the definition of f-invariant entropy to actions of finitely generated virtually free groups. We also obtain a numerical virtual measure conjugacy invariant for actions of finitely generated virtually free groups.

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