[eigen] SVD Bug |

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*To*: Eigen <eigen@xxxxxxxxxxxxxxxxxxx>*Subject*: [eigen] SVD Bug*From*: Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>*Date*: Thu, 23 Sep 2010 12:02:23 +0200*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:received:date:message-id :subject:from:to:content-type; bh=MQOnni14jOGVHtJWVyz2Dyj/y8CAadezT2OnVMrIRD8=; b=nRxSCwBOCkBfnCD0v0sm+engHFvQVEwTtL7rsyG+tEq7EX8EH2tYOjJAV4Mp4AvU8d CoLnuw1hB5kt936OEjuKIM+k7UVpP6Lbz7jm0X9pCYiMQOs4013h+im69Nx1tP/l71uK FTerUWDsZ1psOHGwC9AHkWMa4rsUwkr1z/QjU=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=w/gCZhfrgAT6OOmB3bvdr1vEIa41gLqGnJPIsnXy5QlyjbpBADsKZM7GN8lZK/ncIA jiy4NpAgIcplDte//wWlAlDRVKsy2eNyq63yjd4YkPmd9F478ioCtq1IYQlYuRvdPvq/ rbSxTDhf0Vl05IqnfskUlmFFicAzpxhbcuKl4=

Hi, the user chef_seppel has found a bug in the SVD. Here is the post http://forum.kde.org/viewtopic.php?f=74&t=90425. I can confirm it is a bug. In principle, the attached patch should fix it. I also changed the unit test and according to our docs (http://eigen.tuxfamily.org/dox/classEigen_1_1SVD.html) I would expect any m-by-n matrix A to be working (when m>n). But the unit test fails even for the most simple example where A is 3-by-2, x is 2-by-1 and b is 3-by-1. The failure is caused by the solve part. I tried to look into it but failed. I can only say that already the matrix U is strange since its last row is zero and this should not be the case. I know that Benoit is still working on rewriting the SVD but at least the bad memory access should be fixed. Cheers, Hauke

**Attachment:
svd_fix.patch**

**Follow-Ups**:**Re: [eigen] SVD Bug***From:*Benoit Jacob

**Re: [eigen] SVD Bug***From:*Benoit Jacob

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