We present a method based on Dickson's lemma to compute the" approximate radical" of a
zero dimensional ideal I in C [x 1,..., xm] which has zero clusters: the approximate radical
ideal has exactly one root in each cluster for sufficiently small clusters. Our method is"
global" in the sense that it does not require any local approximation of the zero clusters: it
reduces the problem to the computation of the numerical nullspace of the so called" matrix of
traces", a matrix computable from the generating polynomials of I. To compute the numerical …