Topological invariants of plane curve singularities: Polar quotients and \L ojasiewicz gradient exponents

Abstract

In this paper, we study polar quotients and \L ojasiewicz exponents of plane curve singularities, which are {\em not necessarily reduced}. We first show that the polar quotients is a topological invariant. We next prove that the \L ojasiewicz gradient exponent can be computed in terms of the polar quotients, and so it is also a topological invariant. As an application, we give effective estimates of the \L ojasiewicz exponents in the gradient and classical inequalities of polynomials in two (real or complex) variables.