Thanks a lot - formatting the ordinate as ylim=c(4,10) before plotting pH also removed the problem, and options(digits=10) confirmed that pH was not all exactly 7.4 - as I knew. Still I wonder just why R chooses to plot(ATOT,pH) as shown with repeated "7.4" instead of some more detailed representation. Thanks a gain and happy New Year!
Troels Den 26-12-2017 kl. 01:03 skrev Bert Gunter: > Note that ?all.equal clearly says that it tests for **approximate > equality only** with tolerance "close to 1.5 e-8. > > So.. > > > all.equal(z,pH, tol = 1e-15) > [1] "Mean relative difference: 6.732527e-11" > > and > > > print(pH, digits =15) > ## output omitted > > Shows you what's going on. > > Cheers, > Bert > > > > Bert Gunter > > "The trouble with having an open mind is that people keep coming along > and sticking things into it." > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) > > On Mon, Dec 25, 2017 at 11:00 AM, Troels Ring <tr...@gvdnet.dk > <mailto:tr...@gvdnet.dk>> wrote: > > Dear friends - copy paste missed > > SID <- c() before the first loop - sorry > > BW Troels > > > > Den 25-12-2017 kl. 19:12 skrev Troels Ring: > > > Dear friends - merry Christmas and thanks a lot for much help > during the year! > > In the example below I fail to understand how the calculated > value pH is represented in a simple plot - also included. The > calculations are useful in practice and likely to be right in > principle but I cannot see how this occurs: why a calculated > value of 7.4 known as numeric is not simply plotted as such. > It happened on Windows both 7 and 10 with R version 3.4.1. > > All best wishes > > Troels > > ff <- function(H,SID,ATOT,ka) H + SID - kw/H - ka*ATOT/(H+ka) > ka <- 1e-7 > kw <- 1e-14 > ATOT <- seq(0,0.3,length=100)*1e-3 > > for (i in 1:length(ATOT)) { > SID[i] <- > uniroot(ff,c(-1,1),tol=.Machine$double.eps,maxiter=100000,ka=ka, > ATOT=ATOT[i], H = 10^-7.4)$root} > ATOT > > #confirm pH 0 7.4 > > H <- c() > for (i in 1:length(ATOT)) { > H[i] <- > uniroot(ff,c(1e-19,1),tol=.Machine$double.eps,maxiter=100000,ka=ka, > ATOT=ATOT[i], SID = SID[i])$root} > > (pH <- -log10(H)) > plot(pH) > str(pH) > # num [1:100] 7.4 7.4 7.4 7.4 7.4 ... > z <- rep(7.4,length(ATOT)) > all.equal(z,pH) > #TRUE > points(z,col="red") > > > ______________________________________________ > R-help@r-project.org <mailto:R-help@r-project.org> mailing list -- > To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > <https://stat.ethz.ch/mailman/listinfo/r-help> > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > <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.
