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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] potential bug?
- From: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
- Date: Tue, 3 Aug 2010 14:50:05 -0400
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2010/8/3 Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>:
> Hi,
>
> this code here produces a norm of around 2. Is that a bug or is it me?
>
> - Hauke
>
> #include <Eigen/Eigen>
>
> #include <iostream>
>
> using namespace Eigen;
>
> void main()
> {
> typedef Matrix4d MatrixType;
> MatrixType m = MatrixType::Random();
>
> ColPivHouseholderQR<MatrixType> qr(m);
>
> MatrixType R = qr.matrixQR().triangularView<Upper>();
> MatrixType Q = qr.householderQ();
>
> std::cout << qr.rank() << std::endl;
> std::cout << (Q*R - m).norm() << std::endl;
ColPivHouseholderQR is... pivoting :-)
So you need to apply the permutation if you want to reconstruct the
original matrix.
See the unit-test:
MatrixType r = qr.matrixQR().template triangularView<Upper>();
MatrixType c = q * r * qr.colsPermutation().inverse();
VERIFY_IS_APPROX(m1, c);
Benoit
> }
>
>
>