Wasserstein distance for generalized persistence modules and abelian categories.

In persistence theory and practice, measuring distances between modules is central. The Wasserstein distances are the standard family of L^p distances for persistence modules. They are defined in a combinatorial way for discrete invariants called persistence diagrams that are defined for certain persistence modules. We give an algebraic formulation of these distances that applies to all persistence modules. Furthermore, for p=1 this definition generalizes to abelian categories and for arbitrary p it generalizes to Krull-Schmidt categories. In particular, we obtain a definition of Wasserstein distance for multi-parameter persistence modules. These distances may be useful for the computation of distance between generalized persistence modules. In our most technical proof, we classify certain maps of persistence modules, which may be of independent interest.