Re: [eigen] How to squeeze in place a vector matrix |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] How to squeeze in place a vector matrix*From*: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>*Date*: Wed, 25 Aug 2010 10:54:06 -0400*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=ON6QI8/Vie6Ub/VumNdK7SttwBxk64Bxx4WOrD1jP5w=; b=WaN5grCt/F19qxmNF/V0DROmQ5fXVzZPA9uBh7eSPsvtdhJ0l160yhuJaCHPIE/bJC Ku6hXO5RTXOB4CBqNJDZYYNHHiDAfkFWCRKDOMLGGRLcSAQCLnOWqHQ0lTVxlnm1/ZPQ 6A2yI5rWuy/ytg0WWpZeRNH7HeDm3ajYqQkIk=*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=QCyUMPQLibsVKrluugX8fDkeaAeU5fpeOwo2bmm9NYzlYKIiKFt/HFLvPUR7YIJ843 OqKiSA7FCdZ6pRQiLU6CvdG87ecFz0ziG4c2OgUdnH0rRDe/aL/Azb9DM4/CoBigO5yt UcNSqimsl9zk8KPTEhbZy5mQT+hAQt/JWfayo=

2010/8/25 Bastien ROUCARIES <roucaries.bastien@xxxxxxxxx>: > On Wed, Aug 25, 2010 at 4:18 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote: >> 2010/8/25 Bastien ROUCARIES <roucaries.bastien@xxxxxxxxx>: >>> Hi, >>> >>> I want to squeeze some line and column of matrix in place, in order to >>> remove the null space. >>> >>> How can I do that? >>> >>> I have tryied block(i,j,k,l).eval() but i think it is suboptimal >> >> Ah, I see, trying to avoid aliasing issues. >> >> In fact, in assignments, we are always traversing matrices >> left-to-right and top-to-bottom. >> >> So you can remove the eval() if you are a little careful. For example, >> this works: >> >> matrix.block(i,j,k,l) = matrix.block(i+1,j,k,l); // squeeze row i >> >> Of course this is relying on undocumented behavior; but I really don't >> see why we'd ever change this. > > Because it is really really useful removing null space on eigenvector > decomposition** ? I wasn't questioning the interest of removing null parts of matrices :-) I was saying that the behavior on why my trick above is relying, though undocumented, is unlikely to change. Cheers Benoit > In fact I need to punch out a column/line pair, and it will be really > nice to have a function to punch out in place. > > As you should know null space is evil* :) > > Bastien > > * from a physical point of view :) In fact I am working on the > solution of Ax=lambda B x, and null space does not carry physical > signification and the devil from a numerical point of view > ** computing the resonnance of some physical system. Null space is > due overdetermined limit conidtion > > >

**Follow-Ups**:**Re: [eigen] How to squeeze in place a vector matrix***From:*Bastien ROUCARIES

**References**:**[eigen] How to squeeze in place a vector matrix***From:*Bastien ROUCARIES

**Re: [eigen] How to squeeze in place a vector matrix***From:*Benoit Jacob

**Re: [eigen] How to squeeze in place a vector matrix***From:*Bastien ROUCARIES

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