[R] seq(*,by=) rounding problem {was 'Strange behaviour of "image"'}
Ernesto Jardim
ernesto at ipimar.pt
Thu Oct 3 15:30:41 CEST 2002
Cool !
Thanks
EJ
On Thu, 2002-10-03 at 12:24, Martin Maechler wrote:
> >>>>> "Ernesto" == Ernesto Jardim <ernesto at ipimar.pt>
> >>>>> on 03 Oct 2002 12:11:11 +0100 writes:
>
> Ernesto> Hi I'm using "image" and got some strange
> Ernesto> results. When I define the color sequence as
> Ernesto> "col=gray(seq(0.95,0,-0.01))" or
> Ernesto> "col=gray(seq(0.94,0,-0.01))" I got an error
>
> Ernesto> Error in gray(level) : invalid gray level, must be
> Ernesto> in [0,1].
>
> Ernesto> If I use 0.96 or 0.93 it works ...
>
> yes, this is just floating point arithmetic, or "rounding" :
> The following reveals the problem :
>
> > range(seq(0.94,0, by = -0.01))
> [1] -1.110223e-16 9.400000e-01
> > range(seq(0.93,0, by = -0.01))
> [1] 0.00 0.93
> > range(seq(0.96,0, by = -0.01))
> [1] 0.00 0.96
>
> BTW, I usually never use "by=" in seq() exactly for this reason
> (and rather use "length=" instead).
>
> Martin
> -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
> r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> Send "info", "help", or "[un]subscribe"
> (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch
> _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
More information about the R-help
mailing list