BUSÉ , Laurent

Master

In this habilitation thesis, a matrix-based approach of elimination theory is described and illustrated through applications in algebraic modeling. This matrix-based approach allows to build a bridge between geometry and numerical linear algebra, so that some geometric problems can be given to the powerful numerical linear algebra tools. The...

National audience

Dans cet article, on introduit une nouvelle représentation implicite des courbes et des surfaces paramétrées rationelles, représentation qui consiste pour l'essentiel à les caractériser par la chute de rang d'une matrice plutôt que par l'annulation simultanée d'une ou plusieurs équations polynomiales. On montre comment ces représentations...

In this thesis a theoric and practical study of residual resultant is proposed. This residual resultant provides a necessary and sufficient condition so that an algebraic system has solutions on a residual variety obtained by blowing-up. Effective methods to compute this residual resultant as its degree are exposed, more precise results being...

In this paper, a new kind of resultant, called the determinantal resultant, is introduced. This operator computes the projection of a determinantal variety under suitable hypothesis. As a direct generalization of the resultant of a very ample vector bundle introduced by Gelfand, Kapranov et Zelevinsky, it corresponds to a necessary and...

Le premier chapitre traite du résultant de Sylvester qui constitue l'outil essentiel de ce cours. Le deuxième chapitre propose une étude effective du problème de l'intersection de deux courbes algébriques planes: théorème de Bézout, notion de multiplicité d'intersection et calcul de points d'intersection par valeurs et vecteurs propres. Le...

Ces notes de cours traitent principalement des outils de la géométrie différentielle pour les courbes et surfaces algébriques pour la modélisation des formes.

In this paper, a new kind of resultant, called the determinantal resultant, is introduced. This operator computes the projection of a determinantal variety under suitable hypothesis. As a direct generalization of the resultant of a very ample vector bundle introduced by Gelfand, Kapranov et Zelevinsky, it corresponds to a necessary and...

We introduce and study a new implicit representation of rational Bézier curves and surfaces in the 3-dimensional space. Given such a curve or surface, this representation consists of a matrix whose entries depend on the space variables and whose rank drops exactly on this curve or surface. Our approach can be seen as an extension of the moving...

In this article, we first generalize the recent notion of residual resultant of a complete intersection to the case of a local complete intersection of codimension 2 in the projective plane, which is the necessary and sufficient condition for a system of three polynomials to have a solution ``outside'' a variety, defined here by a local...

In this article, we first generalize the recent notion of residual resultant of a complete intersection to the case of a local complete intersection of codimension 2 in the projective plane, which is the necessary and sufficient condition for a system of three polynomials to have a solution ``outside'' a variety, defined here by a local...

In these notes, we present a general framework to compute the codimension one part of the elimination ideal of a system of homogeneous polynomials. It is based on the computation of the so-called MacRae's invariants that we will obtain by means of determinants of complexes. Our approach mostly uses tools from commutative algebra. We begin with...

We present implementations in both computer systems Macaulay2 and Maple for computing resultant matrices. We give a brief overview of classical resultants, sparse resultants, residual resultants and determinantal resultants, as well as applications and examples using the two presented libraries that we detail in the appendix.

A $d$-dimensional tensor $A$ of format $n\times n\times \cdots \times n$ defines naturally a rational map $\Psi$ from the projective space $\mathbb{P}^{n-1}$ to itself and its eigenscheme is then the subscheme of $\mathbb{P}^{n-1}$ of fixed points of $\Psi$. The eigendiscriminant is an irreducible polynomial in the coefficients of $A$ that...

Given a parametrization of a rational plane algebraic curve C, some explicit adjoint pencils on C are described in terms of determinants. Moreover, some generators of the Rees algebra associated to this parametrization are presented. The main ingredient developed in this paper is a detailed study of the elimination ideal of two homogeneous...

CAD models represented by NURBS surface patches are often hampered with defects due to inaccurate representations of trimming curves. Such defects make these models unsuitable to the direct generation of valid volume meshes, and often require trial-and-error processes to fix them. We propose a fully automated Delaunay-based meshing approach...

Let $P_1,\ldots,P_n$ be generic homogeneous polynomials in $n$ variables of degrees $d_1,\ldots,d_n$ respectively. We prove that if $\nu$ is an integer satisfying ${\sum_{i=1}^n d_i}-n+1-\min\{d_i\}<\nu,$ then all multivariate subresultants associated to the family $P_1,\ldots,P_n$ in degree $\nu$ are irreducible. We show that the lower bound...

In a previous work we introduced a new general representation of algebraic surfaces, that we called semi-implicit, which encapsulates both usual and less known surfaces. Here we specialize this notion in order to apply it in Solid Modeling: we view a surface in the real space as a one-parameter (algebraic) family of algebraic low-degree curves....

In this paper we introduce an intermediate representation of surfaces that we call semi-implicit. We give a general definition in the language of projective complex algebraic geometry, and we begin its systematic study with an effective view point. Our last section will apply this representation to investigate the intersection of two bi-cubic...

We present a subresultant-based algorithm for deciding if the parametrization of a toric hypersurface is invertible or not, and for computing the inverse of the parametrization in the case where it exists. The algorithm takes into account the monomial structure of the input polynomials.

In this paper, we develop a new approach to the discriminant of a complete intersection curve in the 3-dimensional projective space. By relying on the resultant theory, we first prove a new formula that allows us to define this discriminant without ambiguity and over any commutative ring, in particular in any characteristic. This formula also...

In a book dating back to 1862, Salmon stated a formula giving the first terms of the Taylor expansion of the discriminant of a plane algebraic curve, and from it derived various enumerative quantities for surfaces in the 3-dimensional projective space. In this text, we provide complete proofs of this formula and its enumerative applications,...