Persistent Laplacians: Properties, Algorithms and Implications

We present a thorough study of the theoretical properties and devise efficient algorithms for the persistent Laplacian, an extension of the standard combinatorial Laplacian to the setting of pairs (or, in more generality, sequences) of simplicial complexes K,→ L, which was recently introduced by Wang, Nguyen, and Wei. In particular, in analogy with the nonpersistent case, we first prove that the nullity of the qth persistent Laplacian ∆^K,L_q equals the qth persistent Betti number of the inclusion (K,→ L). We then present an initial algorithm for finding a matrix representation of ∆^K,L_q , which itself helps interpret the persistent Laplacian. We exhibit a novel relationship between the persistent Laplacian and the notion of Schur complement of a matrix which has several important implications. In the graph case, it both uncovers a link with the notion of effective resistance and leads to a persistent version of the Cheeger inequality. This relationship also yields an additional, very simple algorithm for finding (a matrix representation of) the qth persistent Laplacian which in turn leads to a novel and fundamentally different algorithm for computing the qth persistent Betti number for a pair K,→ L which can be significantly more efficient than standard algorithms. Finally, we study persistent Laplacians for simplicial filtrations and establish novel functoriality properties and stability results for their eigenvalues. Our work brings methods from spectral graph theory, circuit theory, and persistent homology together with a topological view of the combinatorial Laplacian on simplicial complexes.