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*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=x9wU3QHo431Az5AJQYl8L3s+B2E8tc165Z12fBLPKc4=; b=whlN8ZCzfECnlnbshneh7r7V6/skqGDfQs+jwuNzLHfRLwXxWHLNlfZKft5Fm1Zaon sW6df376IxroQxswbqMcNaB+49+dkL2hZ4O2zCE+n7pmSuZRSN/2QUywl0yQ/BHesdeq tfxcw3VGrwri3GHT0JOTW7s9taNoVGLRfeZJM=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=XdG0J1+RvWMCRqxeUGd6oy2guZovjx+/vrTbkmlTWRNmNg7wEAdU3H+rAQyWR9crhX 9/7KH8W/Kzv0yXqAr1S2TxMys6JeNDE7gPp4NMRaKeONoaklH1W4LIcCAINg1nuxcHku Iz7zfPtgFhymN5FPai0CC+VgsLUkvlRPcHd94=

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! > > > > >

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