La réduction des réseaux. Autour de l'algorithme de Lenstra, Lenstra, Lovász
Dans cet article, nous étudions certains invariants liés à la réduction de Hermite-Korkine-Zolotareff des réseaux euclidens (ou des formes quadratiques définies positives).
We investigate the number of lattice points in special three-dimensional convex bodies. They are called convex bodies of pseudo revolution, because we have in one special case a body of revolution and in another case even a super sphere. These bodies have lines at the boundary, where all points have Gaussian curvature zero. We consider the influence of these points to the lattice rest in the asymptotic representation of the number of lattice points.
Some interesting lattices can be constructed using association schemes. We illustrate this by a unimodular lattice without roots of dimension 28 which admits as its automorphism group.
On montre que le réseau de Barnes-Wall de rang est équivalent au réseau à double congruence de Martinet. La preuve utilise la notion de voisinage de Kneser et des résultats de Koch et Venkov sur le défaut du voisinage (“Nachbardefekt”).
A lattice is called dual strongly perfect if both, the lattice and its dual, are strongly perfect. We show that there are no dual strongly perfect lattices of dimension 13 and 15.
After a brief exposition of the state-of-art of research on the (Euclidean) simultaneous Diophantine approximation constants , new lower bounds are deduced for and .