05C50 05C05 2 05B35 1 15A18 1 47A10 1 47F05 1 Jacobi matrix 1 Smith graphs 1 adjacency matrix 1 adjacency operator 1 co-neighbour vertices 1 conjugate Laplacian matrix 1 cospectral graphs 1 eigenvalue 1 energy 1 forest 1 hypoenergetic graph 1 local equivalence 1 matroid 1 pivot 1 spectral graph theory 1 spectral measure 1 spectral multiplicity function 1 tree 1 unitarily equivalent operators 1