| Re: [eigen] Computing left nullspace of A when rows > cols |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Computing left nullspace of A when rows > cols
- From: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
- Date: Fri, 30 Jan 2009 17:38:22 +0100
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Hi,
The SVD is undergoing a rewrite from scratch for 2.1 so it is a very
good moment to make feature requests.
Can you please tell me what "left nullspace" means ? I'm a "pure"
mathematician so I'm not always aware of the matrix computations
vocabulary.
I wouldn't spend time modifying the existing SVD, instead Keir and me
are going to write a new one as soon as we have time.
Cheers,
Benoit
2009/1/30 W. James MacLean <james.maclean@xxxxxxxxxxx>:
> Hi,
>
> I would like to use Eigen to compute the left nullspace of a matrix A where
> A is n by m, and n > m. Assuming we denote the decomposition as A = U S
> V^*, then (currently) the U returned by Eigen is n by m, and the columns
> corresponding to the left nullspace are missing.
>
> Is it possible to either (1) compute these easily using some other facility
> already in Eigen, or (2) modify Eigen so it outputs the full n by n U
> matrix?
>
> I know that, generally, I could do this by transposing A and computing the
> right nullspace, but then cols > rows and Eigen doesn't seem to support
> this for SVD at present.
>
> Cheers,
>
> James
>
> PS- I *really really* like what I've seen of Eigen so far - way cool!
>
>
>
>
>