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arXiv 1801.06403math.DSmath.AT
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离散动力系统的Conley指标与映射环面

The Conley index for discrete dynamical systems and the mapping torus

Frank Weilandt

摘要:

流的Conley指数是一个拓扑不变量,描述了孤立不变集$S$周围的行为。它被定义为商空间$N/L$的同伦类型,其中$(N,L)$是$S$的索引对。在离散动态系统的情况下,即,连续自映射$f\colon X\to X$,定义类似。但需要考虑由$f$诱导的索引图$f_{(N,L)}\colon N/L\to N/L$。在这种情况下的康利指数被定义为同伦类$[f_{(N,L)}]$模移位等价。移位等价关系很少在此上下文之外使用,并且通常不容易理解。对于实际的目的,如数值计算,需要使用较弱的代数不变量来区分康利指数,通常是同调。这里我们考虑一个拓扑不变量:索引映射$f_{(N,L)}$的映射环面的同伦类型。使用同伦类型提供了新的方法来比较康利指数-理论和数值。我们提出了一些基本的性质和例子,比较它的定义,通过移位等价和素描的想法,其建设使用严格的数值。

英文摘要:

The Conley index for flows is a topological invariant describing the behavior around an isolated invariant set $S$. It is defined as the homotopy type of a quotient space $N/L$, where $(N,L)$ is an index pair for $S$. In the case of a discrete dynamical system, i.e., a continuous self-map $f\colon X\to X$, the definition is similar. But one needs to consider the index map $f_{(N,L)}\colon N/L\to N/L$ induced by $f$. The Conley index in this situation is defined as the homotopy class $[f_{(N,L)}]$ modulo shift equivalence. The shift equivalence relation is rarely used outside this context and not well understood in general. For practical purposes like numerical computations, one needs to use weaker algebraic invariants for distinguishing Conley indices, usually homology. Here we consider a topological invariant: the homotopy type of the mapping torus of the index map $f_{(N,L)}$. Using a homotopy type offers new ways for comparing Conley indices -- theoretically and numerically. We present some basic properties and examples, compare it to the definition via shift equivalence and sketch an idea for its construction using rigorous numerics.

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