Claudia Fassino

Claudia Fassino

Let X be a set of s points whose coordinates are known with only limited From the numerical point of view, given a set X of s real points whose coordinates are known with only limited precision, each set X* of real points whose elements differ from those of X of a quantity less than the data uncertainty can be considered equivalent to X. We present an algorithm that, given X and a tolerance Tol on the data error, computes a set G of polynomials such that each element of G "almost vanishing" at X and at all its equivalent sets X*. Even if G is not, in the general case, a basis of the vanishing ideal I(X), we show that, differently from the basis of I(X) that can be greatly influenced by the data uncertainty, G can determine a geometrical configuration simultaneously characterizing the set X and all its equivalent sets X*.

Claudia Fassino, Maria-Laura Torrente

We present a symbolic-numeric approach for the analysis of a given set of noisy data, represented as a finite set $\X$ of limited precision points. Starting from $\X$ and a permitted tolerance $\varepsilon$ on its coordinates, our method automatically determines a low degree monic polynomial whose associated variety passes close to each point of $\X$ by less than the given tolerance $\varepsilon$.

Claudia Fassino, Stefano Pasquero

We present the algorithmic procedure determining the impulsive behavior of a rigid disk having a single or possibly multiple frictionless impact with two walls forming a corner. The algorithmic procedure represents an application of the general theory of multiple impacts as presented in \cite{Pasquero2016Multiple} for the ideal case. In the first part, two theoretical algorithms are presented for the cases of ideal impact and Newtonian frictionless impact with global dissipation index. The termination analysis of the algorithms differentiates the two cases: in the ideal case, we show that the algorithm always terminates and the disk exits from the corner after a finite number of steps independently of the initial impact velocity of the disk and the angle formed by the walls; in the non--ideal case, although is not proved that the disk exits from the corner in a finite number of steps, we show that its velocity decreases to zero and the termination of the algorithm can be fixed through an "almost at rest" condition. In the second part, we present a numerical version of both the theoretical algorithms that is more robust than the theoretical ones with respect to noisy initial data and floating point arithmetic computation. Moreover, we list and analyze the outputs of the numerical algorithm in several cases.

John Abbott, Claudia Fassino, Maria-Laura Torrente

Let $X$ be a set of points whose coordinates are known with limited accuracy; our aim is to give a characterization of the vanishing ideal $I(X)$ independent of the data uncertainty. We present a method to compute a polynomial basis $B$ of $I(X)$ which exhibits structural stability, that is, if $\widetilde X$ is any set of points differing only slightly from $X$, there exists a polynomial set $\widetilde B$ structurally similar to $B$, which is a basis of the perturbed ideal $ I(\widetilde X)$.

Claudia Fassino

We develop a method for approximating the Gröbner basis of the ideal of polynomials which vanish at a finite set of points, when the coordinates of the points are known with only limited precision. The method consists of a preprocessing phase of the input points to mitigate the effects of the input data uncertainty, and of a new "numerical" version of the Buchberger-Möller algorithm to compute an approximation $\bar{GB}$ to the exact Gröbner basis. This second part is based on a threshold-dependent procedure for analyzing from a numerical point of view the membership of a perturbed vector to a perturbed subspace. With a suitable choice of the threshold, the set $\bar{GB}$ turns out to be a good approximation to a "possible" exact Gröbner basis or to a basis which is an "attractor" of the exact one. In addition, the polynomials of $\bar{GB}$ are "sufficiently near" to the polynomials of the extended basis, introduced by Stetter, but they present the advantage that $LT(\bar{GB})$ coincides with the leading terms of a "possible" exact case. The set of the preprocessed points, approximation to the unknown exact points, is a pseudozero set for the polynomials of $\bar{GB}$.