This file is from Wikimedia Commons and may be used by other projects.
The description on its file description page there is shown below.
Summary
DescriptionHarmonic index.svg
English: Vertices are labeled by their degree. The edges in the graph are labeled 2 divided by the sum of the degrees of vertices incident to it. The Harmonic index is the sum of these edge labels.
The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.
http://creativecommons.org/publicdomain/zero/1.0/deed.enCC0Creative Commons Zero, Public Domain Dedicationfalsefalse
Captions
Vertices are labeled by their [[degree (graph theory)|degree]]. The edges in the graph are labeled 2 divided by the sum of the degrees of vertices [[incidence (graph)|incident]] to it. The '''Harmonic index''' is the sum of these edge labels.