# zbMATH — the first resource for mathematics

Simplicial matrix-tree theorems. (English) Zbl 1207.05227
Summary: We generalize the definition and enumeration of spanning trees from the setting of graphs to that of arbitrary-dimensional simplicial complexes $$\Delta$$, extending an idea due to G. Kalai. We prove a simplicial version of the Matrix-Tree Theorem that counts simplicial spanning trees, weighted by the squares of the orders of their top-dimensional integral homology groups, in terms of the Laplacian matrix of $$\Delta$$. As in the graphic case, one can obtain a more finely weighted generating function for simplicial spanning trees by assigning an indeterminate to each vertex of $$\Delta$$ and replacing the entries of the Laplacian with Laurent monomials. When $$\Delta$$ is a shifted complex, we give a combinatorial interpretation of the eigenvalues of its weighted Laplacian and prove that they determine its set of faces uniquely, generalizing known results about threshold graphs and unweighted Laplacian eigenvalues of shifted complexes.

##### MSC:
 05E45 Combinatorial aspects of simplicial complexes 05A15 Exact enumeration problems, generating functions 05E99 Algebraic combinatorics 05C05 Trees 05C50 Graphs and linear algebra (matrices, eigenvalues, etc.) 15A18 Eigenvalues, singular values, and eigenvectors 57M15 Relations of low-dimensional topology with graph theory
Full Text: