Persistence-perfect discrete gradient vector fields and multi-parameter persistence.

The main objective of this paper is to introduce and study a notion of perfectness for discrete gradient vector fields with respect to (multi-parameter) persistent homology. As a natural generalization of usual perfectness in Morse theory for homology, persistence-perfectness entails having the least number of critical cells relevant for persistent homology. The first result about a persistence-perfect gradient vector-field is that the number of its critical cells yield inequalities bounding the Betti tables of persistence modules, as a sort of Morse inequalities for multi-parameter persistence. The second result is that, at least in low dimensions, persistence-perfect gradient vector-fields not only exist but can be constructed by an algorithm based on local homotopy expansions. These results show a link between multi-parameter persistence and discrete Morse theory that can be leveraged for a better understanding of the former.