@Article{LibeRighSala10,
author = {Federico Liberatore and G. Righini and Matteo Salani },
title = {A column generation algorithm for the vehicle routing problem with soft time windows},
journal = {4OR: A Quarterly Journal of Operations Research},
volume = {9},
number = {1},
pages = {49-82},
doi = {10.1007/s10288-010-0136-6},
year = {2011}
}