Re: [eigen] 3.1.4 & 3.0.7 on Friday? |

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*To*: eigen <eigen@xxxxxxxxxxxxxxxxxxx>*Subject*: Re: [eigen] 3.1.4 & 3.0.7 on Friday?*From*: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>*Date*: Fri, 2 Aug 2013 00:38:08 +0200*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-type; bh=TChtwmCA+zV9NO72Z+o5RoL4VexJytLikwJGEVsXZ9Y=; b=M3XN4tedGTFt9uVJyN4eH09gICNAHEJMGQ1B9tSHsDqawqDs8ndUNkZ5sUMlKrT/2O 4Tc82IqbCPLA3+n+Yf4znF6L7NkC1KVag5AZr7MuCNpoZCvSNl2uhfWh0lh0h9A/MBxZ dZVaoPYPjmme29h4d6psMhJ0615CjoDGlXt6Eiu6zT/gmI+LrGZxosk12YaN8TOLgxT8 MF66mqq7a1Z1OFOalImYH1N2wfKTeWNGEa3QCjgC8H2onnw9ZaFg48Qwf0QEe1jPFMdh 6aZCyGpqx4OngXvHZ9vO/oPhdgvQw7XbGNgY2CF5SFZOvpOJdBSJM3rE/z9guKg/YzEr mZlw==

On Thu, Aug 1, 2013 at 10:24 PM, Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx> wrote: > On Thu, 1 Aug 2013, Rhys Ulerich wrote: > >>>> Running 'EIGEN_SEED=1375367469 >>>> ./build/test/product_trmm_21' causes a repeatable failure for all >>>> compilers tested. >> >> >>> I cannot reproduce. Does it fails for this seed only? >> >> >> It failed on several seeds for me. Using 'while >> ./build/test/product_trmm_21 ; do echo WORKED ; done' will let your >> CPU crank on it until either you find one that breaks or you get bored >> of waiting. > > > I can reproduce it, with the same seed, both for the new 3.1.4 and the > current dev branch. > > I haven't looked at it in detail yet, but the test compares two ways of > computing A - B, where A is a given matrix and B is a product involving a > triangular matrix. For some reason, there is a lot of cancellation going on, > even though these are big random matrices. The norm of A and B are both > about 300, but the norm of A - B is 0.019 and norm of the difference of > computing A - B with both methods is 6e-5 (here, norm is the Kronecker norm, > the sqrt of sum of squares). The test compares 6e-5 with 0.019 and fails, > but arguably it should compare it with 300 and succeed. Yes I came with the same conclusion with a different seed. Surprisingly the cancellation come from the last difference, not the product. So this seems to fix the issue: https://bitbucket.org/eigen/eigen/commits/9de6bcf8bd66/ gael > > So my guess is that the failure is nothing serious, but it's a tad > preliminary at the moment, and I need to stop now. > > > Jitse > >

**References**:**Re: [eigen] 3.1.4 & 3.0.7 on Friday?***From:*Rhys Ulerich

**Re: [eigen] 3.1.4 & 3.0.7 on Friday?***From:*Gael Guennebaud

**Re: [eigen] 3.1.4 & 3.0.7 on Friday?***From:*Rhys Ulerich

**Re: [eigen] 3.1.4 & 3.0.7 on Friday?***From:*Jitse Niesen

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