Re: [eigen] Error: trying to recover Q matrix in sparse QR factorization |

[ Thread Index |
Date Index
| More lists.tuxfamily.org/eigen Archives
]

On 07.05.2013 05:03, Avneesh Saluja wrote:

Hello,
I have a question regarding the sparse QR implementation in the latest
development build of Eigen.
I would like to recover the Q matrix after the factorization, but can't
quite do so. I have followed the suggestion in the following link to get
the SparseMatrix representation of Q (where I assume A is the original
matrix that we are taking the factorization of):
http://eigen.tuxfamily.org/dox-devel/classEigen_1_1SparseQR.html#ac27067ab301641fe6cc35c216a9b18a2

`That looks mostly like a documentation issue. In general, it does not
``make sense to store Q as a sparse matrix, since usually it is not
``anything near sparse. You can directly use qr_factorizer.matrixQ()
``inside expressions. If you really need the actual Q, I guess the
``simplest way would be to multiply by an identity matrix.
`
Christoph
--
----------------------------------------------
Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
Enrique-Schmidt-Straße 5
28359 Bremen
Tel: +49 (421) 218-64252
----------------------------------------------