1. http://www.info.univ-angers.fr/pub/porumbel/graphs/.
2. http://www.boost.org/doc/libs/1_60_0/libs/graph/.
3. https://www.lamsade.dauphine.fr/ magnouche/Instances.zip.
4. https://lemon.cs.elte.hu/trac/lemon.
5. http://www-01.ibm.com/software/integration/optimization/cplex-optimizer/.