Morse Inequalities for Arrangements

Stratified Morse Theory in Arrangements

This paper is a survey of our work based on the stratified Morse theory of Goresky and MacPherson. First we discuss the Morse theory of Euclidean space stratified by an arrangement. This is used to show that the complement of a complex hyperplane arrangement admits a minimal cell decomposition. Next we review the construction of a cochain complex whose cohomology computes the local system cohom...

New inequalities for subspace arrangements

For each positive integer n ≥ 4, we give an inequality satisfied by rank functions of arrangements of n subspaces. When n = 4 we recover Ingleton’s inequality; for higher n the inequalities are all new. These inequalities can be thought of as a hierarchy of necessary conditions for a (poly)matroid to be realizable. Some related open questions about the “cone of realizable polymatroids” are also...

Morse theory, Milnor fibers and hyperplane arrangements

Through the study of Morse theory on the associated Milnor fiber, we show that complex hyperplane arrangement complements are minimal. That is, the complement of any complex hyperplane arrangement has the homotopy type of a CW complex in which the number of p-cells equals the p-th betti number.

Morse Inequalities for a Dynamical System

Witten’s Proof of Morse Inequalities

Both properties do not depend on the choice of coordinates. The index ind (x) is the number of negative eigenvalues of Hess (f) (x). Let mp = mp (f) be the number of critical points of index p. Let bp = bp (M) = dimH (M) be the dimension of the p de Rham cohomology group. 0→ Ω (M) d −→ Ω (M) d −→ ... d −→ Ω (M) d −→ 0 This is called the de Rham complex. Note that d = 0. If ω = dα, then dω = 0. ...