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arXiv math/0604521math.DS
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单项映射的度增长

Degree-growth of monomial maps

Boris Hasselblatt, James Propp

摘要:

对于有理映射的投影化,贝隆和维亚莱用迭代次数的指数增长性定义了代数熵的概念。我们想通过计算射影空间的某些有理映射的代数熵(定理6.2)并将其与拓扑熵(定理5.1)进行比较,来引起动力学家的注意。我们研究的特殊有理映射是单项映射(定义1.2),它与toral自同态密切相关。定理5.1和6.2意味着单项式映射的代数熵总是由它的拓扑熵上有界,并且如果定义矩阵在单位圆之外有多个特征值,则该不等式是严格的。此外,贝隆和维亚莱证明了每一个有理映射的代数熵是一个代数整数的对数,定理6.2为单项式映射建立了这一点。然而,一个简单的例子(例7.2中的单项映射)表明,贝隆和维亚莱的一个更强的猜想是不正确的,因为射影空间的有理映射的迭代的代数次数序列不需要满足常系数的线性递归关系。

英文摘要:

For projectivizations of rational maps Bellon and Viallet defined the notion of algebraic entropy using the exponential growth rate of the degrees of iterates. We want to call this notion to the attention of dynamicists by computing algebraic entropy for certain rational maps of projective spaces (Theorem 6.2) and comparing it with topological entropy (Theorem 5.1). The particular rational maps we study are monomial maps (Definition 1.2), which are closely related to toral endomorphisms. Theorems 5.1 and 6.2 imply that the algebraic entropy of a monomial map is always bounded above by its topological entropy, and that the inequality is strict if the defining matrix has more than one eigenvalue outside the unit circle. Also, Bellon and Viallet conjectured that the algebraic entropy of every rational map is the logarithm of an algebraic integer, and Theorem 6.2 establishes this for monomial maps. However, a simple example (the monomial map of Example 7.2) shows that a stronger conjecture of Bellon and Viallet is incorrect, in that the sequence of algebraic degrees of the iterates of a rational map of projective space need not satisfy a linear recurrence relation with constant coefficients.

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