[Rd] Unexpected behaviour of base::qr()$rank

[Uwe Ligges]

On 22.06.2017 17:11, Bernd Funovits wrote:
> Hello,
> 
> 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
[1] 2.225074e-308


Best,
Uwe Ligges




> 
> Best regards,
> Bernd
> 
>  > R.version
>                 _
> platform       x86_64-w64-mingw32
> arch           x86_64
> os             mingw32
> system         x86_64, mingw32
> status
> major          3
> minor          4.0
> year           2017
> month          04
> day            21
> svn rev        72570
> language       R
> version.string R version 3.4.0 (2017-04-21)
> nickname       You Stupid Darkness
> 
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