Before revision:  There is also a topological view of the graph Laplacian, which permits the extension of the graph Laplacian to the more general q-th combinatorial Laplacian \Delta_q^K for a simplicial complex K.
After revision:  There is also a topological view of the graph Laplacian, which permits thepersistent Laplacian extension of the graph Laplacian to the more general q-th combinatorial Laplacian \Delta_q^K for a simplicial complex K.