Let $X$ be a connected closed manifold and $f$ a self-map on $X$. We say that $f$ is almost quasi-unipotent if every eigenvalue $\lambda$ of the map $f_{*k}$ (the induced map on the $k$-th homology group of $X$) which is neither a root of unity, nor a zero, satisfies that the sum of the multiplicities of $\lambda$ as eigenvalue of all the maps $f_{*k}$ with $k$ odd is equal to the sum of the multiplicities of $\lambda$ as eigenvalue of all the maps $f_{*k}$ with $k$ even. We prove that if $f$ is $C^1$ having finitely many periodic points all of them hyperbolic,...

Soit $f$ un difféomorphisme lisse de ${ℝ}_{+}$ fixant seulement l’origine, et ${𝒵}^r$ son centralisateur dans le groupe des difféomorphismes ${𝒞}^r$. Des résultat classiques de Kopell et Szekeres montrent que ${𝒵}^1$ est toujours un groupe à un paramètre. En revanche, Sergeraert a construit un $f$ dont le centralisateur ${𝒵}^{\infty }$ est réduit au groupe des itérés de $f$. On présente ici le résultat principal de [3] : ${𝒵}^{\infty }$ peut en fait être un sous-groupe propre et non-dénombrable (donc dense) de ${𝒵}^1$.

Consider a bifurcation problem, namely, its bifurcation equation. There is a diffeomorphism $\Phi$ linking the actual solution set with an unfolded normal form of the bifurcation equation. The differential $D\Phi \left(0\right)$ of this diffeomorphism is a valuable information for a numerical analysis of the imperfect bifurcation. The aim of this paper is to construct algorithms for a computation of $D\Phi \left(0\right)$. Singularity classes containing bifurcation points with $\mathrm{c}odim\le 3$, $\mathrm{c}orank=1$ are considered.