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*: Tue, 08 Apr 2014 14:33:35 +0200

On 07.04.2014 20:33, Marc Glisse wrote:

The attached patch doesn't change the result of make check (adolc is still broken, there is a missing -lGL somewhere, and parmetis doesn't chose any MPI so finds none).

http://manao.inria.fr/CDash/testSummary.php?project=1&name=forward_adolc&date=2014-04-08 I don't have METIS installed and strangely, OpenGL is not detected here.

As you can see in LU, there is a subtlety I hadn't thought of: max(abs) was returning a RealScalar, not a Scalar. That's not a big problem when we only want to compare it with 0.

I think I didn't break maxPivot() in FullPivLU.

householder, SVD, etc would likely need a similar treatment.

Of course, but let us do that after we agreed on how to finish this.

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 is better (simplified example). But I agree that simply using the element with the bigger lower bound may not always be the best choice.I believe you need to consider at least a third line. The uncertainty on the pivot will propagate to the whole matrix (except its own row/col).

E.g. choosing a row [(100,100) (-1e6,+1e6) (-2e6,1e3) (-1e3,2e6)]

Is the patch roughly the right approach? Where do we go from there?

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:*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

**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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