Uwe Ligges <[EMAIL PROTECTED]> writes: > Dr Carbon wrote: > > > At the risk of being beaten about the face and body, can somebody explain > > why the middle example: log2(2^3); floor(log2(2^3)) is different than > > examples 1 and 3? > > > Because > > > log2(2^3) - 3 > [1] -4.440892e-16 > > see the R FAQ "Why doesn't R think these numbers are equal?". > > Uwe Ligges
In this particular case, it is slightly odd that we can't get an exact answer for operations that could in principle be carried out using integer arithmetic, but we're actually calculating log(8)/log(2). (Curiously, the same effect is not seen on Linux or Solaris until > log2(2^29)-29 [1] 3.552714e-15 ) > > > >>log2(2^2); floor(log2(2^2)) > > > > [1] 2 > > [1] 2 > > > >>log2(2^3); floor(log2(2^3)) > > > > [1] 3 > > [1] 2 > > > >>log2(2^4); floor(log2(2^4)) > > > > [1] 4 > > [1] 4 > > > > > > DrC > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > R-help@stat.math.ethz.ch mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! > > http://www.R-project.org/posting-guide.html > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
