3.3.1 Maximum independent set heuristics

In addition to the Goemans-Williamson heuristic, two standard heuristics are provided in the corresponding heur.c file. First, in order to obtain an initial solution before we start the Branch-and-Bound method, we go through the vertices of G from lowest degree to highest degree and add a vertex to the independent set if it has no neighbours in the set. Second, during the evaluation of the bound and after running the bounding procedure, follow the same method as the previous heuristic by trying to add each vertex to the independent set given a different order. This time, the order is not actually given by the increasing degree of the vertices but by the fractional solution provided by BiqCrunch (sort the vertices by decreasing fractional value).