Use ?uniroot to do it numerically instead of polyroot()? Cheers, Bert Bert Gunter
"Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." -- Clifford Stoll On Mon, Sep 28, 2015 at 9:17 AM, Ben Bolker <bbol...@gmail.com> wrote: > Dario Strbenac <dstr7320 <at> uni.sydney.edu.au> writes: > >> >> Good day, >> >> I have two probability densities, each with a function determined >> by splinefun(densityResult[['x']], >> densityResult[['y']], "natural"), where densityResult is the >> output of the density function in stats. >> How can I determine all of the x values at which the densities cross ? >> > > My initial thought was this is non-trivial, because the two densities could > cross (or nearly-but-not-quite cross) at an unlimited number of points. > I thought it would essentially boils down to "how do I find all > the roots of an arbitrary (continuous, smooth) function? > > However, after thinking about it for a few more seconds I realize > that at least the functions are piecewise cubic. I still don't see > a *convenient* way to do it ... if the knots were all coincident between > the two densities (maybe you could constrain them to be so?) then you > just have a difference of cubics within each segment, and you can use > polyroot() to find the roots (and throw out any that are complex or > don't fall within the segment). > If the knots are not coincident it's more of a pain but you should > still be able to do it by considering overlapping segments ... > > ______________________________________________ > 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. ______________________________________________ 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.
