Proof of the gradient conjecture of R. Thom.
Ensembles semi-algébriques symétriques par arcs.
An arc-analytic function with nondiscrete singular set
We construct an arc-analytic function (i.e. analytic on every real-analytic arc) in ℝ² which is analytic outside a nondiscrete subset of ℝ².
A counterexample to subanalyticity of an arc-analytic function
We construct an arc-analytic function (i.e. a function analytic on each analytic arc) whose graph is not subanalytic.
On gradients of functions definable in o-minimal structures
We prove the o-minimal generalization of the Łojasiewicz inequality , with , in a neighborhood of , where is real analytic at and . We deduce, as in the analytic case, that trajectories of the gradient of a function definable in an o-minimal structure are of uniformly bounded length. We obtain also that the gradient flow gives a retraction onto levels of such functions.
Points réguliers d'un sous-analytique
On donne une autre démonstration (sans désingularisation de Hironaka) du théorème de Tamm, qui dit que la partie régulière d’un sous-analytique est sous-analytique. En plus, on montre que pour chaque fonction de classe SUBB (“sous-analytique à l’infini”), où est un sous-ensemble ouvert et borné dans , il existe un entier tel que est analytique dans si et seulement si est de classe (-fois différentiable au sens de Gateaux) dans un voisinage de .
Surjectivity of Certain Injective Semialgebraic Transformations of IRn.
Subanalytic version of Whitney's extension theorem
For any subanalytic -Whitney field (k finite), we construct its subanalytic -extension to . Our method also applies to other o-minimal structures; e.g., to semialgebraic Whitney fields.
O-minimal version of Whitney's extension theorem
This is a generalized and improved version of our earlier article [Studia Math. 124 (1997)] on the Whitney extension theorem for subanalytic -Whitney fields (with p finite). In this new version we consider Whitney fields definable in an arbitrary o-minimal structure on any real closed field R and obtain an extension which is a -function definable in the same o-minimal structure. The Whitney fields that we consider are defined on any locally closed definable subset of Rⁿ. In such a way, a local...
Densité des ensembles sous-analytiques
It is shown that a sub-analytic set has a density at each point, and the notion of pure cone is defined. As in the complex case, this density may be expressed in terms of the area of the connected components of the pure tangent cone, with involved integral multiplicities.
Explicit bounds for the Łojasiewicz exponent in the gradient inequality for polynomials
Let f: ℝⁿ → ℝ be a polynomial function of degree d with f(0) = 0 and ∇f(0) = 0. Łojasiewicz’s gradient inequality states that there exist C > 0 and ϱ ∈ (0,1) such that in a neighbourhood of the origin. We prove that the smallest such exponent ϱ is not greater than with .
An inverse mapping theorem for arc-analytic homeomorphisms
We show that a subanalytic map-germ (Rⁿ,0) → (Rⁿ,0) which is arc-analytic and bi-Lipschitz has an arc-analytic inverse.
Sum of squares and the Łojasiewicz exponent at infinity
Let V ⊂ ℝⁿ, n ≥ 2, be an unbounded algebraic set defined by a system of polynomial equations and let f: ℝⁿ→ ℝ be a polynomial. It is known that if f is positive on V then extends to a positive polynomial on the ambient space ℝⁿ, provided V is a variety. We give a constructive proof of this fact for an arbitrary algebraic set V. Precisely, if f is positive on V then there exists a polynomial , where are sums of squares of polynomials of degree at most p, such that f(x) + h(x) > 0 for x...
Gradient horizontal de fonctions polynomiales
Nous étudions les trajectoires du gradient sous-riemannien (appellé horizontal) de fonctions polynômes. Dans ce cadre l’inégalité de Łojasiewicz n’est pas valide et une trajectoire du gradient horizontal peut être de longueur infinie, et peut même s’accumuler sur une courbe fermée. Nous montrons que ces comportement sont exceptionnels ; et que, pour une fonction générique les trajectoires de son gradient horizontal ont des propriétés similaires au cas du gradient riemannien. Pour obtenir la finitude...
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