LFD Book Forum How Many Iterations to Pick Best K-Cluster?
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#1
09-17-2012, 05:34 PM
 DavidNJ Member Join Date: Jul 2012 Posts: 28
How Many Iterations to Pick Best K-Cluster?

To pick the best set of K-Means clusters centroids for each training set, how many times should be generate the centroids to find the best? 10? 100? 1000? The higher number provides the higher probability of finding the the centroids with the lowest Eout.

Thanks,

David
#2
09-17-2012, 06:00 PM
 MLearning Senior Member Join Date: Jul 2012 Posts: 56
Re: How Many Iterations to Pick Best K-Cluster?

Quote:
 Originally Posted by DavidNJ To pick the best set of K-Means clusters centroids for each training set, how many times should be generate the centroids to find the best? 10? 100? 1000? The higher number provides the higher probability of finding the the centroids with the lowest Eout. Thanks, David
You need a condition that stops iteration when the centroids do not change.
#3
09-17-2012, 06:31 PM
 DavidNJ Member Join Date: Jul 2012 Posts: 28
Re: How Many Iterations to Pick Best K-Cluster?

Different problem If you start with different initial centroids you get different results. If you run it enough you can materially change Ein and Eout because of a better centroid result.

By itself K-means clustering doesn't guarantee an optimal result although it reaches a stable result quickly (especially with so few data points).
#4
09-17-2012, 08:05 PM
 MLearning Senior Member Join Date: Jul 2012 Posts: 56
Re: How Many Iterations to Pick Best K-Cluster?

Quote:
 Originally Posted by DavidNJ Different problem If you start with different initial centroids you get different results. If you run it enough you can materially change Ein and Eout because of a better centroid result. By itself K-means clustering doesn't guarantee an optimal result although it reaches a stable result quickly (especially with so few data points).
I agree that K-means clustering is locally optimal.
#5
09-18-2012, 12:06 AM
 rainbow Member Join Date: Jul 2012 Posts: 41
Re: How Many Iterations to Pick Best K-Cluster?

It was mentioned in lectures that you in general should try different initilizations.

However, I didn't do this... I just started with K random real data points. This strategy favours the SVM model when we compare classification performance, but since we execute the experiment many times this type of bias should be diminishing.
#6
09-18-2012, 04:37 AM
 DavidNJ Member Join Date: Jul 2012 Posts: 28
Re: How Many Iterations to Pick Best K-Cluster?

I'm getting a difference of two letters in the answer between using the first k-means cluster returned and testing 50 clusters per training data set.

If I can't get an official answer....those who submitted the correct answer, was it one iteration or a high number of iterations to choose the centroids for RBF?

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