Continuous functions on the plane regular after one blowing-up

Goulwen Fichou (1) , Ronan Quarez (1) , Jean-Philippe Monnier (2)

1 IRMAR - Institut de Recherche Mathématique de Rennes
2 LAREMA - Laboratoire Angevin de Recherche en Mathématiques

We study rational functions admitting a continuous extension to the real affine space. First of all, we focus on the regularity of such functions exhibiting some nice properties of their partial derivatives. Afterwards, since these functions correspond to rational functions which become regular after some blowings-up, we work on the plane where it suffices to blow-up points and then we can count the number of stages of blowings-up necessary. In the latest parts of the paper, we investigate the ring of rational continuous functions on the plane regular after one stage of blowings-up. In particular, we prove a Positivstellensatz without denominator in this ring.

Mots clés: sum of squares; real algebraic variety; rational function; regular function; regulous function

Domaines: Géométrie algébrique [math.AG]

Goulwen Fichou, Ronan Quarez, Jean-Philippe Monnier. Continuous functions on the plane regular after one blowing-up. Mathematische Zeitschrift, 2017, 285 (1), pp.287-323. ⟨10.1007/s00209-016-1708-8⟩. ⟨hal-01069575⟩