  In the recent years, the trace norm of graphs has been extensively studied
under the name of graph energy. In this paper some of this research is extended
to more general matrix norms, like the Schatten p-norms and the Ky Fan k-norms.
Whenever possible the results are given both for graphs and general matrices.
In various contexts a puzzling fact was observed: the Schatten p-norms are
widely different for 1<=p<2 and for p>=2.
