Re: [eigen] 3.1.4 & 3.0.7 on Friday?

[Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx>]

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.

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