ELKI OPTICSXi - how set xi?
cluster-analysis, data-mining, elki, optics-algorithm
Solution
You can read up on the Xi parameter in
Mihael Ankerst, Markus M. Breunig, Hans-Peter Kriegel, Jörg Sander (1999). OPTICS: Ordering Points To Identify the Clustering Structure ACM SIGMOD international conference on Management of data. ACM Press. pp. 49–60.
it is a contrast parameter, the relative decrease in density. I usually try values such as 0.1 (= 10% drop in density). However, the exact drop in density to be expected heavily depends on your data set and parameters, for obvious reasons.
Problem
I'm trying to use ELKI to cluster a dataset of geolocations using OPTICS. I've understood that to extract the clusters, I need to use the OPTICSXi algorithm rather than OPTICS which computes just the clusters order. I was wondering if you could give me more information on how the parameter xi works. I fixed this value at 0.009 but in a random way.