Steven D. Noble, Pierre Hansen, Nenad Mladenovic. Maximizing edge-ratio is NP-complete. Discrete Applied Mathematics, 159(18):2276-2280, 2011. [doi]
@article{NobleHM11,
title = {Maximizing edge-ratio is NP-complete},
author = {Steven D. Noble and Pierre Hansen and Nenad Mladenovic},
year = {2011},
doi = {10.1016/j.dam.2011.07.016},
url = {http://dx.doi.org/10.1016/j.dam.2011.07.016},
researchr = {https://researchr.org/publication/NobleHM11},
cites = {0},
citedby = {0},
journal = {Discrete Applied Mathematics},
volume = {159},
number = {18},
pages = {2276-2280},
}