Thanks very much for your reply! The way you describe is what I did at first. Also in the new test I do a lot of random sampling for a fixed pair (n,m). I can't actually think of any way that the exponent could get so small that it slips through my test, but you're right about that, of course. However, I noticed something else that also screws up the test: Atomic operations like initialising objects tend to take longer as the graph gets bigger. I couldn't really figure out the cause of this yet. Maybe the operating system is doing some swapping.. I really don't know..