Stability of non-proper functions

Kenta Hayano

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arXiv · 1809.02332

Stability of non-proper functions

Kenta Hayano

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Abstract

The purpose of this paper is to give a sufficient condition for (strong) stability of non-proper smooth functions (with respect to the Whitney $C^\infty$-topology). We show that a Morse function is stable if it is end-trivial at any point in its discriminant, where end-triviality (which is also called local triviality at infinity) is a property concerning behavior of functions around the ends of the source manifolds. We further show that a Morse function $f:N\to \mathbb{R}$ is strongly stable (i.e. there exists a continuous mapping $g\mapsto (Φ_g,ϕ_g)\in\operatorname{Diff}(N)\times \operatorname{Diff}(\mathbb{R})$ such that $ϕ_g\circ g\circ Φ_g =f$ for any $g$ close to $f$) if (and only if) $f$ is quasi-proper. This result yields existence of a strongly stable but not infinitesimally stable function. Applying our result on stability, we give a reasonable sufficient condition for stability of Nash functions, and show that any Nash function becomes stable after a generic linear perturbation.

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BibTeX RIS

Kenta Hayano. 2021-04-16. Stability of non-proper functions. https://arxiv.org/abs/1809.02332

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