[Rd] Unexpected behaviour of base::qr()$rank
i.ucar86 at gmail.com
Thu Jun 22 20:09:18 CEST 2017
2017-06-22 19:49 GMT+02:00 Uwe Ligges <ligges at statistik.tu-dortmund.de>:
> On 22.06.2017 17:11, Bernd Funovits wrote:
>> I experienced some unexpected behaviour while determining the rank of matrices (sometimes 1x1 matrices):
>> base::qr(matrix(1e-20))$rank returns 1 (incorrect)
>> base::qr(diag(c(1, 1e-20)))$rank returns 2 (incorrect)
> Why do you believe this is incorrect?
> 0 != 1e-20
> and 1e-20 is well representable without significant rounding errors given
> > .Machine$double.xmin
>  2.225074e-308
> Uwe Ligges
qr() has a tolerance argument which by default is tol=1e-07.
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