Splines over integer quotient rings

Abstract

Given a graph with edges labeled by elements in $\mathbb{Z}/m\mathbb{Z}$, a generalized spline is a labeling of each vertex by an integer $\mod m$ such that the labels of adjacent vertices agree modulo the label associated to the edge connecting them. These generalize the classical splines that arise in analysis as well as in a construction of equivariant cohomology often referred to as GKM-theory. We give an algorithm to produce minimum generating sets for the $\mathbb{Z}$-module of splines on connected graphs over $\mathbb{Z}/m \mathbb{Z}$. As an application, we give a quick heuristic to determine the minimum number of generators of the module of splines over $\mathbb{Z}/m\mathbb{Z}$. We also completely determine the ring of splines over $\mathbb{Z}/p^k\mathbb{Z}$ by providing explicit multiplication tables with respect to the elements of our minimum generating set. Our final result extends some of these results to splines over $\mathbb{Z}$.