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Si Tiep Dinh; Krzysztof Kurdyka; Patrice Orro Gradient horizontal de fonctions polynomiales (Horizontal gradient of polynomial functions) Annales de l'institut Fourier, 59 no. 5 (2009), p. 1999-2042, doi: 10.5802/aif.2481 Article: subscription required (your ip address: 107.22.156.205) | Reviews MR 2573195 | Zbl 1197.14058 Class. Math.: 14P10, 53C17, 58Kxx, 58A30, 58K14, 93F14 Keywords: Sub-Riemannian, gradient, inegality Résumé - Abstract We study trajectories of sub-Riemannian (also called horizontal) gradient of polynomials. In this setting Łojasiewicz’s gradient inequality does not hold and a trajectory of a horizontal gradient may be of infinite length, moreover it may accumulate on a closed curve. We show that these phenomena are exceptional; for a generic polynomial function the behavior of the trajectories of horizontal gradients are similar to the behavior of the trajectories of a Riemannian gradient. To obtain the finiteness of the length of trajectories we change suitably the sub-Riemannian metric. We consider a class of splitting distributions which contains those of Heisenberg and Martinet. For a generic polynomial $f$ the set $V_f$ of horizontal critical points, is a smooth algebraic set of dimension $1$ or the empty set, moreover $f|_{V_f}$ is a Morse function. We show that for a generic polynomial function any trajectory of the horizontal gradient (which approaches $V_f$) has a limit, as in the Riemannian case studied by S. Łojasiewicz. Bibliography Article | MR 2225367 | Zbl 1129.34320 [2] M. Baeg, U. Helmke & J. B. Moore, Gradient flow techniques for pose estimation of quadratic surfaces, in Proceedings of the World Congress in Computational Methods and Applied Mathematics, 1994 [3] Z. M. Balogh, I. Holopainen & J. T. Tyson, “Singular solutions, homogeneous norms, and quasiconformal mappings in Carnot groups”, Math. 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