Fast In-place Algorithms for Polynomial Operations: Division, Evaluation, Interpolation

We consider space-saving versions of several important operations on univariate polynomials, namely power series inversion and division, division with remainder, multi-point evaluation, and interpolation. Now-classical results show that such problems can be solved in (nearly) the same asymptotic time as fast polynomial multiplication. However, these reductions, even when applied to an in-place variant of fast polynomial multiplication, yield algorithms which require at least a linear amount of extra space for intermediate results. We demonstrate new in-place algorithms for the aforementioned polynomial computations which require only constant extra space and achieve the same asymptotic running time as their out-of-place counterparts. We also provide a precise complexity analysis so that all constants are made explicit, parameterized by the space usage of the underlying multiplication algorithms

On the Geometry and the Topology of Parametric Curves

International audienceWe consider the problem of computing the topology and describing the geometry of a parametric curve in R. We present an algorithm, PTOPO, that constructs an abstract graph that is isotopic to the curve in the embedding space. Our method exploits the benefits of the parametric representation and does not resort to implicitization. Most importantly, we perform all computations in the parameter space and not in implicit space. When the parametrization involves polynomials of degree at most and maximum bitsize of coefficients , then the worst case bit complexity of PTOPO is O (6 + 5 + 4 (2 +) + 3 (2 + 3) + 3 2). This bound matches the current record bound O (6 + 5) for the problem of computing the topology of a planar algebraic curve given in implicit form. For planar and space curves, if = max{ , }, the complexity of PTOPO becomes O (6), which improves the state-of-the-art result, due to Alcázar and Díaz-Toca [CAGD'10], by a factor of 10. However, visualizing the curve on top of the abstract graph construction, increases the bound to O (7). We have implemented PTOPO in maple for the case of planar curves. Our experiments illustrate its practical nature

Algorithmes rapides pour les polynômes, séries formelles et matrices

Notes d'un cours dispensé aux Journées Nationales du Calcul Formel 2010International audienceLe calcul formel calcule des objets mathématiques exacts. Ce cours explore deux directions : la calculabilité et la complexité. La calculabilité étudie les classes d'objets mathématiques sur lesquelles des réponses peuvent être obtenues algorithmiquement. La complexité donne ensuite des outils pour comparer des algorithmes du point de vue de leur efficacité. Ce cours passe en revue l'algorithmique efficace sur les objets fondamentaux que sont les entiers, les polynômes, les matrices, les séries et les solutions d'équations différentielles ou de récurrences linéaires. On y montre que de nombreuses questions portant sur ces objets admettent une réponse en complexité (quasi-)optimale, en insistant sur les principes généraux de conception d'algorithmes efficaces. Ces notes sont dérivées du cours " Algorithmes efficaces en calcul formel " du Master Parisien de Recherche en Informatique (2004-2010), co-écrit avec Frédéric Chyzak, Marc Giusti, Romain Lebreton, Bruno Salvy et Éric Schost. Le support de cours complet est disponible à l'url https://wikimpri.dptinfo.ens-cachan.fr/doku.php?id=cours:c-2-2