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.