These are not the algorithms but an overview of the formulas.<p>For example the HN algorithm is outlined in several places e.g. <a href="http://news.ycombinator.com/item?id=38704" rel="nofollow">http://news.ycombinator.com/item?id=38704</a> and on the pg Arc site, and the reddit algorithms is<p><pre><code> def hot(ups, downs, date):
s = score(ups, downs)
order = log(max(abs(s), 1), 10)
sign = 1 if s > 0 else -1 if s < 0 else 0
seconds = epoch_seconds(date) - 1134028003
return round(order + sign * seconds / 45000, 7)</code></pre>
Use of true clock time in these formulas penalizes posts that are submitted at low-traffic times.<p>Using a virtual clock, such as a tick count based on traffic (number of other submissions, votes, pageviews, etc.), could adjust for this.
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.<p>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.<p>For the SU one, I think there is more to the story, but that's for another post...
Yippee! Thats great. But how did u findout delicious's and stumbleupon's? By reverse engineering technique... like... Were these found out(or guess-worked) by constantly keeping track of the ranking of content?<p>Joshu, i think the del.icio.us formula is right, or they might just be using a different time constraint than 1 hour(maybe 2hrs or anything else). Because to findout what's popular they dont require any complex stuff. Simple math as specified in Danny's post is enough for their task.<p>Go Danny! Go!!!