Monday, October 21, 2013

Application of clustering

Informal goal - given n points [web pages images, genome fragments, etc] classify into "coherent groups"
People in machine learning must have heard of unsupervised learning.
1) As input, given a (dis) similarity measure
2 symmetric

examples - euclidean distance, genome similarity

goal - same clusters => nearby

So, coherent group has smaller distance.

Objective function to do clustering - there are many objective functions, but we are reading max-spacing k-clusterings. 

Max spacing  k-clustering
Assume we know  k = number of clusters desired
[In practice, can experiment with a range of values]

Call points p and q seperated if they are assigned to different clusters.

Problem statement - given a distance d and k, compute the k-clustering with maximum spacing.

greedy algorithm




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