On Gradient Dynamical Systems

TLDR: In this article, the authors consider a Co vector field X on a Co compact manifold Mn and show that if x at x is transversal (not tangent) to SM, then X is not zero on SM.

Abstract: We consider in this paper a Co vector field X on a Co compact manifold Mn (&M, the boundary of M, may be empty or not) satisfying the following conditions: (1) At each singular point /8 of X, there is a cell neighborhood N and a Co function f on N such that X is the gradient of f on N in some riemannian structure on N. Furthermore /8 is a non-degenerate critical point of f. Let ,81 , m denote these singularities. (2) If x e &M, X at x is transversal (not tangent) to SM. Hence X is not zero on SM. (3) If x e M let p,(x) denote the orbit of X (solution curve) through x satisfying p0(x) = x. Then for each x e M, the limit set of p,(x) as t +-~ oo is contained in the union of the /3i. (4) The stable and unstable manifolds of the /3i have normal intersection with each other. This has the following meaning. The stable manifold Wj* of /3i is the set of all x e M such that limits ...p,(x) = /i. The unstable manifold Wi of 8i is the set of all x e M such that limit,,-,. t(x) = /i. It follows from conditions (1), (2) and a local theorem in [1, p. 330], that if /3i is a critical point of index X, then Wi is the image of a 1-1, Co map pi: U-s M, where Uc Rn A has the property if x e U, tx e U, 0 ? t ? 1 and pi has rank n X everywhere (see [4] for more details). A similar statement holds for Wi* with the U c RA. Now for x e Wi (or Wi*) let Wi2, (or We*) be the tangent space of Wi (or Wi*) at x. Then for each i, j, if x e Wf nWj*, condition (4) means that