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Date: Fri, 09 Sep 2011 06:55:45 -0700
From: Phil Steitz <phil.steitz@gmail.com>
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To: Commons Developers List <dev@commons.apache.org>
Subject: Re: [Math] "LUDecomposition" in "AbstractLeastSquaresOptimizer"
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On 9/9/11 6:00 AM, Gilles Sadowski wrote:
> Hi.
>
> On Thu, Sep 08, 2011 at 10:27:00AM -0500, Greg Sterijevski wrote:
>> Could you be contaminating the cross product matrix when you do your
>> accumulation? I noticed one of the utility classes has methods for doing
>> safe accumulations. I know that this was part of the problem when I was
>> trying to estimate the Wampler data with the MillerRegression. Just a
>> thought...
> To make sure, I've tried replacing the "sum" calculation in "getCovariances"
> with one using "linearCombination for "MathUtils" but it still fails, so it
> seems that the (default) threshold is too small, and I need to be able to
> change it.

Could be the best thing to do here is to make the
DecompositionSolver pluggable (maybe just for the LMOptimizer, but
with hooks in the base class)?  That way you could provide an LU
solver with whatever threshold you want or choose among the others. 
Do you know if the jTj matrix you end up trying to invert is
analytically singular (like the one in the testNonInvertible test
case for LMOptimizer)?

Phil
>
>
> Regards,
> Gilles
>
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