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From Aniruddha Basak <t-aba...@expedia.com>
Subject Mahout LanczosSolver explanation
Date Wed, 01 Aug 2012 01:00:15 GMT
Hi,
I am working on Spectral Kmeans which involves an eigen-decomposition step
using Lanczos. As I did not get exact similar results as expected, I tried to understand the
implementation.
I have one question about "LanczosSolver .java" :
In the "solve" method, while building the "tridiagonal matrix" there is a step just
after the multiplication job (performed on Hadoop as TimesSquaredJob) as
------------
nextVector.assign(new Scale(1.0 / state.getScaleFactor()));
-----------
I could not understand why this scaling is performed?

( When I compared the results on a small matrix to an equivalent Matlab script,
I found the results are exactly similar WITHOUT this scaling. Including this scaling
makes the results different from the Matlab results.  )


Thanks,
Aniruddha


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