{ "id": "0905.3944", "version": "v2", "published": "2009-05-25T04:53:05.000Z", "updated": "2009-05-26T01:37:54.000Z", "title": "Hypoenergetic and strongly hypoenergetic trees", "authors": [ "Xueliang Li", "Hongping Ma" ], "comment": "8 pages", "categories": [ "math.CO" ], "abstract": "The energy $E(G)$ of a graph $G$ is defined as the sum of the absolute values of the eigenvalues of $G$. An $n$-vertex graph is said to be hypoenergetic if $E(G)