Thank you to all who have made great suggestions. Both Gabor and David's
methods work well for me. I see now where I was going wrong with this, I
wasn't loading it to a function. I also did not know expression could be
used in that way.

Thank you very much for your help!

Katrina

On Fri, Nov 18, 2011 at 6:02 AM, Gabor Grothendieck <ggrothendieck@gmail.com
> wrote:

> On Thu, Nov 17, 2011 at 4:40 PM, Katrina Bennett <kebennett@alaska.edu>
> wrote:
> > Hello, I am wondering if someone can help me. I have the following
> function
> > that I derived using nls() SSlogis. I would like to find its derivative.
> I
> > thought I had done this using deriv(), but for some reason this isn't
> > working out for me.
> >
> > Here is the function:
> > asym <- 84.951
> > xmid <- 66.90742
> > scal <- -6.3
> >
> > x.seq <- seq(1, 153,, 153)
> > nls.fn <- asym/((1+exp((xmid-x.seq)/scal)))
> >
> > try #1
> > deriv(nls.fn)
> > #get an Error in .Internal(deriv.default(expr, namevec, function.arg,
> tag,
> > hessian)) : 'namevec' is missing
> >
> > try #2
> > deriv(nls.fn, namevec=c("asym", "xmid", "scal"))
> > #this doesn't seem to give me the expression, and the gradients are zero.
> >
> > I've tried to do this with Ryacas as well, but I'm lost.
> >
> > Can anyone help?
> >
>
> You can do that with plain R:
>
> > e <- quote(asym/((1+exp((xmid-x.seq)/scal))))
> > for(v in all.vars(e)) cat("deriv wrt", v, "is", format(D(e, v)), "\n")
> deriv wrt asym is 1/((1 + exp((xmid - x.seq)/scal)))
> deriv wrt xmid is -(asym * (exp((xmid - x.seq)/scal) * (1/scal))/((1 +
> exp((xmid -      x.seq)/scal)))^2)
> deriv wrt x.seq is asym * (exp((xmid - x.seq)/scal) * (1/scal))/((1 +
> exp((xmid -      x.seq)/scal)))^2
> deriv wrt scal is asym * (exp((xmid - x.seq)/scal) * ((xmid -
> x.seq)/scal^2))/((1 +      exp((xmid - x.seq)/scal)))^2
>
>
> --
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
> tel: 1-877-GKX-GROUP
> email: ggrothendieck at gmail.com
>



-- 
Katrina E. Bennett
PhD Student
University of Alaska Fairbanks
International Arctic Research Center
930 Koyukuk Drive, PO Box 757340
Fairbanks, Alaska 99775-7340
907-474-1939 office
907-385-7657 cell
kebennett@alaska.edu


Personal Address:
UAF, PO Box 752525
Fairbanks, Alaska 99775-2525
bennett.katrina@gmail.com

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