And, for crying out loud... just try it with x = 1.234e-16 or so. One would think that the hint |x| << 1 was obvious enough.
-pd > On 12 Dec 2016, at 18:26 , William Dunlap via R-help <r-help@r-project.org> > wrote: > > 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. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Office: A 4.23 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ 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.
