On May 5, 2014, at 6:05 PM, Gabor Grothendieck wrote: > On Mon, May 5, 2014 at 9:43 AM, Niloofar.Javanrouh > <javanrou...@yahoo.com> wrote: >> >> >> hello, >> i want to differentiate of L with respect to b >> when: >> >> L= k*ln (k/(k+mu)) + sum(y) * ln (1-(k/mu+k)) #(negative binomial ln >> likelihood) >> and >> ln(mu/(mu+k)) = a+bx #link function >> >> how can i do it in R? > > Try this. First we solve for 'mu' in terms of the other variables > using the link equation: > >> library(Ryacas) >> k <- Sym("k") >> mu <- Sym("mu") >> y <- Sym("y") >> L <- Sym("L") >> a <- Sym("a") >> b <- Sym("b") >> x <- Sym("x") >> sumy <- Sym("sumy") >> Solve(log(mu/(mu+k)) == a+b*x, "mu") > expression(list(mu == k * exp(a + b * x)/(1 - exp(a + b * x)))) >> > > Now in 'k*log(k/(k+mu)) + sumy * log(1-(k/mu+k))' substitute 'k * > exp(a + b * x)/(1 - exp(a + b * x)))' for 'mu' using 'Subst' and take > the derivative with respect to 'a' using 'deriv': > >> s <- Subst(k*log(k/(k+mu)) + sumy * log(1-(k/mu+k)), mu, > + k * exp(a + b * x)/(1 - exp(a + b * x))) >> deriv(s, a) > expression(sumy * (k * ((1 - exp(a + b * x)) * (k * exp(a + b * > x)) + k * exp(a + b * x)^2))/((1 - exp(a + b * x))^2 * (k * > exp(a + b * x)/(1 - exp(a + b * x)))^2 * (1 - (k * (1 - exp(a + > b * x))/(k * exp(a + b * x)) + k))) - k * ((k + k * exp(a + > b * x)/(1 - exp(a + b * x))) * (k * ((1 - exp(a + b * x)) * > (k * exp(a + b * x)) + k * exp(a + b * x)^2)))/((1 - exp(a + > b * x))^2 * ((k + k * exp(a + b * x)/(1 - exp(a + b * x)))^2 * > k))) >
But can we maybe get the Taylor series approximation to first or second order? -- David Winsemius Alameda, CA, USA ______________________________________________ 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.