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From Aniruddha Basak <>
Subject RE: Mahout LanczosSolver explanation
Date Wed, 01 Aug 2012 01:28:00 GMT
I did not choose Lanczos. It found it being used as a part of Spectral-Kmeans
implemented in Mahout.
Can u please recommend some better alternative of Lanczos.


-----Original Message-----
From: Ted Dunning [] 
Sent: Tuesday, July 31, 2012 6:24 PM
Cc: Jake Mannix
Subject: Re: Mahout LanczosSolver explanation

WHy are you using Lanczos?  Why not use something more recent?

On Tue, Jul 31, 2012 at 7:00 PM, Aniruddha Basak <>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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