Hostname: page-component-848d4c4894-nr4z6 Total loading time: 0 Render date: 2024-05-31T13:54:03.051Z Has data issue: false hasContentIssue false

On the Euler characteristic of semi-analytic and semi-algebraic sets

Published online by Cambridge University Press:  24 October 2003

NICOLAS DUTERTRE
Affiliation:
Centre de Recerca Matemàtica, Institut d'Estudis Catalans, Apartat 50, E-08193 Bellaterra, España. e-mail: dutertre@crm.es

Abstract

We consider an analytic function-germ $f{:}\,(\mathbb{R}^n,0) \rightarrow (\mathbb{R},0)$ with an isolated critical point at $0$. For a sufficiently small ball $B_\varepsilon$ of radius $\varepsilon$ and a sufficiently small regular value $\delta$ of $f$, we give degree formulas for the following Euler–Poincaré characteristics: $$\chi( f^{-1}(\delta) \cap B_\varepsilon \cap \{(-1)^{\epsilon_1} x_1\ge 0,\ldots, (-1)^{\epsilon_k} x_k \ge 0\}),$$ where $k \in \{1,\ldots,n\}$ and $\epsilon_i \in \{0,1\}$. This leads to degree formulas for $$ \chi (\{f * 0\} \cap S_\varepsilon \cap \{(-1)^{\epsilon_1} x_1\ge 0,\ldots, (-1)^{\epsilon_k} x_k \ge 0\}),$$ where $* \in \{\le,=,\ge\}$. Combining this with the Eisenbud–Levine–Khimshiashvili's formula, we obtain signature formulas for $$\chi( W \cap\{(-1)^{\epsilon_1} x_1\ge 0,\ldots, (-1)^{\epsilon_k} x_k \ge 0\}),$$ where $W$ is either the link of a weighted-homogeneous singularity or any compact algebraic set of $\mathbb{R}^n$.

Type
Research Article
Copyright
© 2003 Cambridge Philosophical Society

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)