05C50 15A18 6 05C05 3 tree 3 05C15 2 05C25 2 05C30 2 05C31 2 05C85 2 20D99 2 47A10 2 Jacobi matrix 2 adjacency operator 2 co-neighbour vertices 2 commuting graph 2 conjugate Laplacian matrix 2 cospectral graphs 2 cospectral signed digraphs 2 eigenvalues of graphs 2 finite group 2 integral graph 2 interval 2 interval edge coloring 2 maximum degree 2 normal signed digraph 2 path cover number and domination number of a graph 2 proper edge coloring 2 spectral graph theory 2 spectral measure 2 spectral multiplicity function 2