Re: [eigen] Specializing max_coeff_visitor for some number types |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] Specializing max_coeff_visitor for some number types*From*: Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>*Date*: Mon, 07 Apr 2014 16:23:18 +0200

On 07.04.2014 15:38, Marc Glisse wrote:

On Mon, 7 Apr 2014, Christoph Hertzberg wrote:I would rather suggest to out-factor a method find_best_pivot which then can be specialized for special types.At what point exactly should it split? The easiest would be that LU calls: DenseBase<Derived>::bestPivotCoeff(IndexType* index) const which visits with a best_coeff_visitor, which uses internal::scalar_better_coeff_op, which by default compares the absolute values. But then we lost the parallelism in computing the absolute values.

For interval types, I guess the element with the biggest lower bound is generally to be preferred (however it depends on if you want to determine the best possible decomposition for a given matrix, or the worst-case scenario what could happen when decomposing with standard floating point types).I want the best in my case (well, not necessarily the best, but one good enough). And the biggest lower-bound is just a simple heuristic, given the choice between (1,1) and (2,20) I'd pick the first interval as the better pivot ;-) But it may not be worth doing anything more subtle.

Hm, well the question is for a matrix, e.g., [ (1,1) row1 ] [ (2,20) row2 ] whether row2 - (2,20)/(1,1) * row1 or row1 - (1,1)/(2,20) * row2

Christoph -- ---------------------------------------------- Dipl.-Inf., Dipl.-Math. Christoph Hertzberg Cartesium 0.049 Universität Bremen Enrique-Schmidt-Straße 5 28359 Bremen Tel: +49 (421) 218-64252 ----------------------------------------------

**Follow-Ups**:**Re: [eigen] Specializing max_coeff_visitor for some number types***From:*Christoph Hertzberg

**Re: [eigen] Specializing max_coeff_visitor for some number types***From:*Marc Glisse

**References**:**[eigen] Specializing max_coeff_visitor for some number types***From:*Marc Glisse

**Re: [eigen] Specializing max_coeff_visitor for some number types***From:*Christoph Hertzberg

**Re: [eigen] Specializing max_coeff_visitor for some number types***From:*Marc Glisse

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