English

Removing Isolated Zeroes by Homotopy

Geometric Topology 2020-01-27 v2 Complex Variables

Abstract

Suppose that the inverse image of the zero vector by a continuous map f:RnRqf:{\mathbb R}^n\to{\mathbb R}^q has an isolated point PP. There is a local obstruction to removing this isolated zero by a small perturbation, generalizing the notion of index for vector fields, the q=nq=n case. The existence of a continuous map gg which approximates ff but is nonvanishing near PP is equivalent to a topological property we call "locally inessential," and for dimensions nn, qq where πn1(Sq1)\pi_{n-1}(S^{q-1}) is trivial, every isolated zero is locally inessential. We consider the problem of constructing such an approximation gg, and show that there exists a continuous homotopy from ff to gg through locally nonvanishing maps. If ff is a semialgebraic map, then there exists such a homotopy which is also semialgebraic. For q=2q=2 and ff real analytic with a locally inessential isolated zero, there exists a H\"older continuous homotopy F(x,t)F(x,t) which, for (x,t)(P,0)(x,t)\ne(P,0), is real analytic and nonvanishing. The existence of a smooth homotopy, given a smooth map ff, is stated as an open question.

Keywords

Cite

@article{arxiv.1712.01787,
  title  = {Removing Isolated Zeroes by Homotopy},
  author = {Adam Coffman and Jiří Lebl},
  journal= {arXiv preprint arXiv:1712.01787},
  year   = {2020}
}

Comments

to appear in Topological Methods in Nonlinear Analysis

R2 v1 2026-06-22T23:07:40.442Z