David Winsemius wrote: > > On Nov 30, 2008, at 10:23 PM, Dylan Beaudette wrote: > >> Hi, I am using the rcs() function in the Design library to model >> non-linearity that is not well characterized by an otherwise >> mechanistic function. I am able to make the model 'available' to >> others through the excellent nomogram() function and the set of tables >> that it can create. However, I would like to present the model in an >> 'expanded' format-- probably what rcspline.restate() or latex.Design() >> produce on a model fit object. >> >> Here is how the model was fit: >> >> fit.ols <- ols( log(k) ~ (rcs(activity) * (log(conc) + sar)) + >> (rcs(sand) * (log(conc) + sar)), data=sm.clean, x=TRUE, y=TRUE) >> >> Here is how I am accessing the 'expanded' format of the model structure: >> >> options(digits=3) >> latex(fit.ols, file='fit_rcs.tex') >> >> The output contains several notation elements that I am not familiar >> with: >> >> 1. x_{+} --> it seems that this represent a term that should be set >> to 0, when x is 0? > > It is set to zero when the term inside the cubic is less than zero. See > pages 20-21 of Harrell's book where the basis functions are described > and illustrated. >> >> i.e. the entire expression −453(activity − 0.842)_{+}^{3} = 0 when >> 'activity' = 0 ?? > > .... whenever (activity − 0.842) < 0 > > > >> >> 2. the '!x' found in : >> >> +log(conc) [ −0.0118sand + 9.58 >> ! × >> !10−6 (sand − 11.6) > > My guess is that this is 9.58 x 10^-6 >> >> − 0.000128(sand − 37.5) >> +0.00045(sand − 47.2) >> − 0.000350(sand − 51) >> + 1.86 >> ! × >> !10−5 (sand − 69.8) ] > > I don't see anything like that in Harrell's text and I am wondering if a > different character is getting rendering incorrectly. The only time you > see it is when the exponent is below -4. > > >> >> >> >> .... what exactly does that mean? >> >> >> An image version of the equation in question is attached. >> >> Any input would be greatly appreciated! >> >> Cheers, >> >> Dylan
Thanks for the good reply David. There is a bug in one of the Hmisc functions regarding the ! spacing command. If you get any LaTeX syntax errors I can send you the correction. Frank >> <complex_equation.png>______________________________________________ >> R-help@r-project.org mailing list >> 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. > > ______________________________________________ > R-help@r-project.org mailing list > 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. > -- Frank E Harrell Jr Professor and Chair School of Medicine Department of Biostatistics Vanderbilt University ______________________________________________ R-help@r-project.org mailing list 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.