precision in seq

FAQ Q7.31 and ?"==" should enlighten you.

None of 0.05, 0.1 ... 0.9, 0.95 are exactly representable on a binary 
computer.

Hi everybody,

this is a warning more than a question.

I noticed that seq produces approximate results:

seq(0,1,0.05)[19]==0.9
[1] TRUE
seq(0,1,0.05)[20]==0.95
[1] FALSE
seq(0,1,0.05)[21]==1
[1] TRUE

seq(0,1,0.05)[20]-0.95
[1] 1.110223024625157e-16

I do not understand why 0.9 and 1 are correct (within some
tolerance or strictly exact?)  and 0.95 is not.

this one works:

((0:20)/20)[20]==0.95
[1] TRUE

Eric Elguero

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

precision in seq

Thread (8 messages)