"make check" fails on lapack.R and stats-Ex.R

Hi Martyn,

Thanks for the analysis on that, and I'll remember that test in future - I've not seen a rounding error quite so finely balanced before. I've been using the "-fp-model precise" advice referenced in that document for a while - apparently it wasn't sufficient for this case.

Thanks also to Brian for sanity checking the linear algebra results in a previous post, and apologies for my imprecise terminology.

Regards,
Mike.

-----Original Message-----
From: Martyn Plummer [mailto:plummerm at iarc.fr] 
Sent: 23 October 2014 10:46
To: Pacey, Mike
Cc: r-devel at r-project.org
Subject: Re: [Rd] "make check" fails on lapack.R and stats-Ex.R

As my attachment doesn't seem to have survived transit, I'm cut'n'pasting the relevant failures here:

Testing examples for package 'stats'
  comparing 'stats-Ex.Rout' to 'stats-Ex.Rout.save' ...
6466c6466
< Grand Mean: 291.5937
---

Grand Mean: 291.5938

I see the same thing, but it is not as bad as it looks. The actual value is 291.59375 so a small amount of numerical error can make the rounding to 4 decimal places go either way:

print(fit[[1]]$coefficients, digits=16)

(Intercept)
291.5937500000002 

Note that MKL sacrifices reproducibility (and hence precision) for speed. See more details here:

https://software.intel.com/en-us/articles/run-reproducibility-with-intel-mkl-and-the-intel-compilers

Martyn