According to the documentation arcost should be the costs associated
with ARCs which makes the number double the number of edges in the
undirected graph. Keep in mind that perfect_match only accepts
undirected graphs as input.
What I am unable to figure out is that what order should I specify the
costs in? Lets say I have 24 edges so that size of arcost needs to be
48. Once I specify the cost of the edges in the same sequence as I
specified the edges, I then have 24 arcs with costs. What order should I
follow for the other direction?