[pierrefar]

For reddit, this is the public algo released with their code. I think we should not assume that's the algo they use on reddit.com. Think about it: they could easily release a basic algo and keep the good one for their own internal use.

At the very least, even reddit's blog post announcement of the code mentioned they're not open sourcing the spam detection code. Surely that's part of the ranking algo in that it determines if a submission gets ranked or not.

For the SU one, I think there is more to the story, but that's for another post...

[pg]

I don't think they'd bother trying to fake people out by releasing a different ranking algorithm than they used on the site. There wouldn't be any point anyway. Knowing how to get onto the frontpage of a venetian-blind site like Digg might be useful to spammers, but knowing the ranking algorithm of a bubble-up site like Reddit or News.YC wouldn't help them much.

[Raphael]

It really doesn't get much better than (p - 1)/t^n, where n is larger if you want age to be more of a handicap.