Attempt nswap double-edge swaps on the graph G.
Return count of successful swaps. The graph G is modified in place. A double-edge swap removes two randomly choseen edges u-v and x-y and creates the new edges u-x and v-y:
u--v u v
becomes | |
x--y x y
If either the edge u-x or v-y already exist no swap is performed so the actual count of swapped edges is always <= nswap
Does not enforce any connectivity constraints.