You are most definitely not wrong. I would have expected some mention of the spectrum of a graph beyond simply defining what the eigenvalues are.
Incidentally, one interesting thing about the graph spectrum is that it's actually not a very interesting invariant. Among other things, almost all trees are cospectral, as proven in the following paper by Allen Schwenk in 1973: https://www.researchgate.net/publication/245264768_Almost_al...
Incidentally, one interesting thing about the graph spectrum is that it's actually not a very interesting invariant. Among other things, almost all trees are cospectral, as proven in the following paper by Allen Schwenk in 1973: https://www.researchgate.net/publication/245264768_Almost_al...