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From Ted Dunning <ted.dunn...@gmail.com>
Subject Re: Mahout LanczosSolver explanation
Date Wed, 01 Aug 2012 01:24:12 GMT
WHy are you using Lanczos?  Why not use something more recent?

On Tue, Jul 31, 2012 at 7:00 PM, Aniruddha Basak <t-abasak@expedia.com>wrote:

> 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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