RE: [eigen]

["SHIROKOBROD Oleg" <Oleg.Shirokobrod@xxxxxxxxxx>]

Thanks Benoit,

 

Oleg

 

 

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From: Listengine [mailto:listengine@xxxxxxxxxxxxxxxxx] On Behalf Of Benoit Jacob
Sent: Sunday, May 30, 2010 18:04
To: eigen@xxxxxxxxxxxxxxxxxxx
Subject: Re: [eigen]

 

aaahh... this had me puzzled for a while, but what you really have here is an aliasing problem. With the devel branch, when you do S = S.inverse(), S starts being overwritten with its inverse and then read again to compute the rest of the inverse... i need to have a look at the code to see if we're getting any speed gain from that, a priori i'd say let's work like in 2.0, taking care of aliasing, and if later there is demand for a super optimized noalias variant, we can then add it with an explicit name like a.noalias()  = a.inverse(), like for products.

Benoit

2010/5/28 SHIROKOBROD Oleg <Oleg.Shirokobrod@xxxxxxxxxx>

Hello,

 

I’ve met a problem with development branch. Here you are the case.

                                   { -2.0                                     -1.0 }

I have a 2x2 matrix S = {                                                   }

                                   { 0.00026130287408377900     -2.0 }

 

and I want to inverse it. This is the code I compiled with MSVS 2008

 

#include <Eigen\Core>

#include <Eigen\LU>

 

Eigen::Matrix<double, 2, 2> S;

S << -2.0 , -1.0 , 0.00026130287408377900 , -2.0;

S = S.inverse();

 

Eigen2 gives the right answer

 

{-0.499967339	0.24998367}
S.inverse  =  {
{-6.53215E-05	-0.499967339}

 

 

Eigen3 (development branch I got on 26.05) gives a wrong answer

 

 

{-0.499967339	0.24998367}
S.inverse  =  {
{-6.53215E-05	-0.124983670170524}

 

 

What’s wrong?

 

Thank you,

 

Oleg Shirokobrod

 

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