On Wednesday, 18 September 2013 at 17:13:28 UTC, bearophile wrote:
How many times or how often do you need to call betweenness()? If it's called only few times or once in a while then using the GC is good enough. But if you have to call it many millions of times, all those GC array allocations could cost some time, even if they are small arrays. In this case allocating them on the stack (or not allocating them, using externally allocated buffers) helps.
I think millions of times is excessive. In my test code I have an example with a 50-node network calculating betweenness centrality 10000 times, which takes under 1.5 seconds. So obviously if you scale up to millions, small improvements could make a difference, but it's not going to be on such a scale that it's worth prioritizing, at least for now. I think even 10000 calculations is excessive for any practical case I can think of.
You're right to call for the opportunity to pass a buffer, though, and I've enabled that. In the current test code it doesn't seem to improve anything, but that may be simply a matter of scale.
