On Thu, 7 Aug 2003 13:44:19 -0700, Sean Chittenden <[EMAIL PROTECTED]> wrote: >> The indexCorrelation^2 algorithm was only a quick hack with no theory >> behind it :-(. I've wanted to find some better method to put in there, >> but have not had any time to research the problem. > >Could we "quick hack" it to a geometric mean instead since a mean >seemed to yield better results than indexCorrelation^2?
Linear interpolation on (1-indexCorrelation)^2 (algorithm 3 in http://members.aon.at/pivot/pg/16-correlation-732.diff) is almost as good as geometric interpolation (algorithm 4 in the patch, proposal 3 in this thread), and its computation is much cheaper because it does not call exp() and log(). Download http://members.aon.at/pivot/pg/cost_index.sxc and play around with your own numbers to get a feeling. (1-indexCorrelation)^2 suffers from the same lack of theory behind it as indexCorrelation^2. But the results look much more plausible. Well, at least to me ;-) Servus Manfred ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org
