>>>>> peter dalgaard <pda...@gmail.com>
>>>>> on Fri, 16 Sep 2016 13:33:11 +0200 writes:
> On 16 Sep 2016, at 12:41 , Alexis Sarda <alexis.sa...@gmail.com> wrote:
>> Hello,
>>
>> while testing the crossprod() function under Linux, I noticed the
following:
>>
>> set.seed(883)
>> x <- rnorm(100)
>> x %*% x - sum(x^2) # equal to 1.421085e-14
>>
>> Is this difference normal? It seems to be rather large for double
precision.
>>
> It's less than .Machine$double.eps, relative (!) to x %*% x ~= 100.
indeed!
Still, it gives exactly 0 on my platform(s), where I'm using R's
own version of BLAS / Lapack.
Are you perhaps using an "optimized" BLAS / LAPACK , i.e, one
that is fast but slightly less so accurate ?
Martin Maechler,
ETH Zurich
> -pd
>> Regards,
>> Alexis.
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-devel@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
> --
> Peter Dalgaard, Professor,
> Center for Statistics, Copenhagen Business School
> Solbjerg Plads 3, 2000 Frederiksberg, Denmark
> Phone: (+45)38153501
> Office: A 4.23
> Email: pd....@cbs.dk Priv: pda...@gmail.com
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
