Thanks, but my problem is that I have my formulas in functions. How can I do that for functions or e.g. for the body(Df) below? And: How can I refer to the first solution of expression? Thanks a lot!
-----Ursprüngliche Nachricht----- Von: Gabor Grothendieck [mailto:ggrothendi...@gmail.com] Gesendet: Donnerstag, 26. August 2010 14:56 An: Immanuel Seeger Cc: r-help@r-project.org Betreff: Re: [R] equalize function with zero and convert it On Thu, Aug 26, 2010 at 6:57 AM, Immanuel Seeger <jimmy-see...@web.de> wrote: > Dear all, > I want to equalize a symbolic derivative (of a function with two > variables) with zero and convert it to a variable, e.g. x. > > I'm computing the derivative by: (found it in the archive) > library(Ryacas) > f <- function(x,y) (100-x-y)*x-10*x > yacas(f) # register f with yacas > Df <- f > body(Df) <- yacas(expression(deriv(f(x,y),x)))[[1]] > Df > > R-Output: > function (x, y) > 100 - x - y - x - 10 > > Questions : > 1. How can I equalize the derivative(140-x-y-x-20) with zero? > 2. How can I convert it to x? > > I want something like: > 45-0.5*y=x > > With only one variable or two non-symbolic variables it's working with > uniroot(f, c(-10, 10))$root. > This solves for x: > library(Ryacas) Loading required package: XML > x <- Sym("x") > y <- Sym("y") > Solve((100-x-y)*x-10*x == 0, "x") [1] "Starting Yacas!" expression(list(x == -((10 - (100 - y) + root((100 - y - 10)^2, 2))/2), x == -((10 - (100 - y) - root((100 - y - 10)^2, 2))/2))) -- GKX Group GKX Associates Inc. 1-877-GKX-GROUP ggrothendieck at gmail.com ______________________________________________ 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.
