For my own edification more than anything (I never took computer science): is
> a = seq(0.1,0.9,by=0.1) > a <- as.character(a) > a[3] == "0.3" [1] TRUE safe? -Ista On Wed, Sep 30, 2009 at 3:46 PM, cls59 <ch...@sharpsteen.net> wrote: > > > Martin Batholdy wrote: >> >> hum, >> >> can you explain that a little more detailed? >> Perhaps I miss the background knowledge - but it seems just absurd to >> me. >> >> 0.1+0.1+0.1 is 0.3 - there is no rounding involved, is there? >> >> > > Unfortunately this comes as an utter shock to many people who never take a > Computer Science course. I watch it nail engineering students all the time. > > Basically, if you have a fraction and the denominator is not equal to 2^n > for some integer n, that fraction will NEVER be stored as an exact "floating > point" number-- instead it will contain some error due to concessions that > must be made in order to use an efficient binary number scheme. > > These errors are generally small, but they do propagate-- especially if you > are carrying the same numbers through a large computation. A good example is > large-scale numerical solutions to nonlinear problems where iterative > algorithms are employed repetitively at each solution step. As the > calculation progresses the roundoff error can rot away the computational > soundness of the algorithm. > > If this concerns you, I would suggest reading up on common internal > representations of floating point numbers as well as the propagation of > roundoff error. > > At the very least I hope this revelation will instill an appropriate sense > of paranoia concerning the numbers calculated by those magic boxes sitting > on our desks. > > -Charlie > > ----- > Charlie Sharpsteen > Undergraduate > Environmental Resources Engineering > Humboldt State University > -- > View this message in context: > http://www.nabble.com/Rounding-error-in-seq%28...%29-tp25686630p25687626.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@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. > -- Ista Zahn Graduate student University of Rochester http://yourpsyche.org ______________________________________________ R-help@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.