Samuel Fiorini, Gianpaolo Oriolo, Laura Sanità , Dirk Oliver Theis. The VPN Problem with Concave Costs. SIAM J. Discrete Math., 24(3):1080-1090, 2010. [doi]
@article{FioriniOST10,
title = {The VPN Problem with Concave Costs},
author = {Samuel Fiorini and Gianpaolo Oriolo and Laura Sanità and Dirk Oliver Theis},
year = {2010},
doi = {10.1137/090749700},
url = {http://dx.doi.org/10.1137/090749700},
researchr = {https://researchr.org/publication/FioriniOST10},
cites = {0},
citedby = {0},
journal = {SIAM J. Discrete Math.},
volume = {24},
number = {3},
pages = {1080-1090},
}