> On Apr 6, 2018, at 8:03 AM, David Winsemius <dwinsem...@comcast.net> wrote: > > >> On Apr 6, 2018, at 3:43 AM, g l <gnuli...@gmx.com> wrote: >> >>> Sent: Friday, April 06, 2018 at 5:55 AM >>> From: "David Winsemius" <dwinsem...@comcast.net> >>> >>> >>> Not correct. You already have `predict`. It is capale of using the >>> `newdata` values to do interpolation with the values of the coefficients in >>> the model. See: >>> >>> ?predict >>> >> >> The ยง details did not mention interpolation explicity; thanks. >> >>> The original question asked for a derivative (i.e. a "gradient"), but so >>> far it's not clear that you understand the mathematical definiton of that >>> term. We also remain unclear whether this is homework. >>> >> >> The motivation of this post was simple differentiation of a tangent point >> (dy/dx) manually, then wondering how to re-think in modern-day computing >> terms. Hence the original question about asking the appropriate >> functions/syntax to read further ("curiosity"), not the answer (indeed, >> "homework"). :) >> >> Personal curiosity should be considered "homework". > > Besides symbolic differentiation, there is also the option of numeric > differentiation. Here's an amateurish attempt: > > myNumDeriv <- function(x){ (exp( predict (graphmodeld, > newdata=data.frame(t=x+.0001))) - > exp( predict (graphmodeld, > newdata=data.frame(t=x) )))/ > .0001 } > myNumDeriv(c(100, 250, 350))

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I realized that this would not work in the context of your construction. I had earlier made a more symbolic version using R formulae: graphdata<-read.csv(text='t,c 0,100 40,78 80,59 120,38 160,25 200,21 240,16 280,12 320,10 360,9 400,7') graphmodeld<-lm(log(c)~t, graphdata) graphmodelp<-exp(predict(graphmodeld)) plot(c~t, graphdata) lines(graphdata[,1],graphmodelp) myNumDeriv(c(100, 250, 350), graphmodeld ) #---------------------------------------------- 1 2 3 -0.31464102 -0.11310753 -0.05718414 > > > > David Winsemius > Alameda, CA, USA > > 'Any technology distinguishable from magic is insufficiently advanced.' > -Gehm's Corollary to Clarke's Third Law > > ______________________________________________ > 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 Alameda, CA, USA 'Any technology distinguishable from magic is insufficiently advanced.' -Gehm's Corollary to Clarke's Third Law ______________________________________________ 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.