[R] seq(*,by=) rounding problem {was 'Strange behaviour of "image"'}

[Ernesto Jardim]

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
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