David, I did read the help page. All it says is log1p(x) computes log(1+x) accurately also for |x| << 1 (and less accurately when x is approximately -1). This gives me pause. Does it mean that log(x) does not give accurate results? If log1p gives more accurate values than log, why is the log function not written to use the more accurate computation performed by log1p. I don't believe I can look directly at the code for log and log1p, so I need to rely on the kindness of others to explain the differences between the computations performed by the functions. I guess the test I ran, log1p(0.000001)/log(0.000001+1), did not have enough precision to demonstrate a difference between the two functions. 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) >>> David Winsemius <dwinsem...@comcast.net> 12/12/16 12:05 PM >>> > On 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 Read the help page more carefully. -- David. > > > 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 the sole use of > the intended recipient(s) and may contain confidential and privileged > information. Any unauthorized use, disclosure or distribution is > prohibited. If you are not the intended recipient, please contact the > sender by reply email and destroy all copies of the original message. > ______________________________________________ > 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. David Winsemius the intended recipient(s) and may contain confidential and privileged information. Any unauthorized use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. ______________________________________________ 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.
