Print more digits of the quotient or subtract one from it and you will see the difference:
> log1p(0.000001)/log(0.000001+1) - 1 [1] 8.22666379463044e-11 Bill Dunlap TIBCO Software wdunlap tibco.com On Mon, Dec 12, 2016 at 8:53 AM, John Sorkin <jsor...@grecc.umaryland.edu> wrote: > At the risk of being flamed . . . > What is the difference between log1p(x) and log(x+1)? > The two methods appear to give the same results: > > log1p(0.000001)/log(0.000001+1) > [1] 1 > John > > > John David Sorkin M.D., Ph.D. > Professor of Medicine > Chief, Biostatistics and Informatics > University of Maryland School of Medicine Division of Gerontology and > Geriatric Medicine > Baltimore VA Medical Center > 10 North Greene Street > GRECC (BT/18/GR) > Baltimore, MD 21201-1524 > (Phone) 410-605-7119 > (Fax) 410-605-7913 (Please call phone number above prior to faxing) > > >>> William Dunlap via R-help <r-help@r-project.org> 12/12/16 11:38 AM >>> > log1p(x), in the base package computes log(1+x) accurately for small x (and > large). > > E.g., > > options(digits=16) > > base::log1p(1e-14) > [1] 9.99999999999995e-15 > > base::log1p(1e-14) - base::log(1+1e-14) > [1] 7.992778373591124e-18 > > as.numeric(log(Rmpfr::mpfr(1,precBits=1000) + Rmpfr::mpfr(1e-14, > precBits=1000))) - log1p(1e-14) > [1] 0 > > > Bill Dunlap > TIBCO Software > wdunlap tibco.com > > On Mon, Dec 12, 2016 at 8:23 AM, Faradj Koliev <farad...@gmail.com> wrote: > > > Hi all, > > > > How do I perform log(x+1) in R? > > > > log1p_trans() from the package ”scales" doesn’t seem to work for me. > > > > Best, > > Faradj > > ______________________________________________ > > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > > 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. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. > > *Confidentiality Statement:* > > This email message, including any attachments, is for ...{{dropped:10}} ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
