Gradient-like vector field

In differential topology, a mathematical discipline, and more specifically in Morse theory, a gradient-like vector field is a generalization of gradient vector field.

The primary motivation is as a technical tool in the construction of Morse functions, to show that one can construct a function whose critical points are at distinct levels. One first constructs a Morse function, then uses gradient-like vector fields to move around the critical points, yielding a different Morse function.

Definition

Given a Morse function f on a manifold M, a gradient-like vector field X for the function f is, informally:

away from critical points, X points "in the same direction as" the gradient of f, and
near a critical point (in the neighborhood of a critical point), it equals the gradient of f, when f is written in standard form given in the Morse lemmas.

Formally:[https://books.google.com/books?id=TtKyqozvgIwC&pg=PA63 p. 63]

away from critical points, $X \cdot f > 0,$
around every critical point there is a neighborhood on which f is given as in the Morse lemmas:

: $f(x) = f(b) - x_1^2 - \cdots - x_{\alpha}^2 + x_{\alpha +1}^2 + \cdots + x_n^2$

and on which X equals the gradient of f.

Dynamical system

The associated dynamical system of a gradient-like vector field, a gradient-like dynamical system, is a special case of a Morse–Smale system.

References

An introduction to Morse theory, Yukio Matsumoto, 2002, Section 2.3: Gradient-like vector fields, [https://books.google.com/books?id=TtKyqozvgIwC&pg=PA56 p. 56–69]
[http://hilbertthm90.wordpress.com/2009/09/25/gradient-like-vector-fields-exist/ Gradient-Like Vector Fields Exist] {{Webarchive|url=https://web.archive.org/web/20120326013348/http://hilbertthm90.wordpress.com/2009/09/25/gradient-like-vector-fields-exist/ |date=2012-03-26 }}, September 25, 2009

Category:Morse theory

Category:Differential topology