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https://issues.apache.org/jira/browse/MAHOUT-518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12917263#action_12917263
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Shannon Quinn commented on MAHOUT-518:
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This is worth discussion: Eigencuts (and spectral clustering algorithms on a
whole) is designed to work specifically on images, but in theory can be used
for any general-purpose clustering if the data format is correct. The primary
issue here, however, is that the input affinity matrix A currently must be
symmetrical (and sparse, but that's the Mahout requirement). The symmetry is
easy to do with images: the general rule of thumb is that for each pixel, the
neighborhood of affinities consists of the 8 pixels around it, therefore making
it both sparse and symmetric. Were these data points to be drawn from arbitrary
distributions (say, a bunch of points in Euclidean space), you can picture
instances where the neighborhoods of nearest data points aren't symmetric.
There are optimizations that can be made to convert non-symmetric input data
into lower-rank approximations that are fully symmetric, but that's probably
something we should tackle later (there's a section on this problem
specifically in Dr. Chennubhotla's thesis containing Eigencuts, that's probably
a good place to start). My recommendation for this ticket is to allow the
algorithm to process raw images; generalized input data (which is not
necessarily symmetric) can come later.
My only point regarding images is that for most academic purposes, this
algorithm has used input images in PGM format; problem is, Java doesn't have a
native PGM image processor, hence why I'm still tweaking the Eigencuts
examples. If anyone knows of something that would help with this, please let me
know.
> Implement Affinity Preprocessing for Eigencuts and Spectral KMeans
> ------------------------------------------------------------------
>
> Key: MAHOUT-518
> URL: https://issues.apache.org/jira/browse/MAHOUT-518
> Project: Mahout
> Issue Type: Improvement
> Components: Clustering
> Affects Versions: 0.4
> Reporter: Jeff Eastman
> Fix For: 0.5
>
>
> The input format for these clustering algorithms is currently affinity
> tuples. It would be very nice to have this process automated. Marking for 0.5
> as this will require some investigation.
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