I just realized that I was actually using a different random number
generator, could that be a valid reason for the discrepancy?
The code should be:
x <- rnorm(100)
x %*% x - sum(x^2) # equal to 1.421085e-14
On Tue, Sep 20, 2016 at 5:27 PM, Martin Maechler <maech...@stat.math.ethz.ch
> >>>>> 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>
> >> Hello,
> >> while testing the crossprod() function under Linux, I noticed the
> >> 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
> > It's less than .Machine$double.eps, relative (!) to x %*% x ~= 100.
> 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]]
> >> ______________________________________________
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> > --
> > Peter Dalgaard, Professor,
> > Center for Statistics, Copenhagen Business School
> > Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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> > Email: pd....@cbs.dk Priv: pda...@gmail.com
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