Re: [R] help with nls and Hill equation

I think its your parameterization that is problematic. ED50^hill is tough for it to work with since both are varying. Try reparameterizing using ED50hill = ED50^hill as a parameter so that the parameters become Emax, ED50hill and hill. You can back transform afterwards. On 10/16/07, Lanre Oku

Re: [R] help with nls and Hill equation

On Tue, Oct 16, 2007 at 10:29:17AM -0400, Lanre Okusanya wrote: > Thanks. > I am just not used to having such a huge difference when changing the > initial condition by 1 point. it usually tends to be an issue when you > are way off (especially since the hill converged at 1.69). Does it > have some

Re: [R] help with nls and Hill equation

riginal Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Christian Ritz Sent: Tuesday, October 16, 2007 10:01 AM To: Lanre Okusanya Cc: [EMAIL PROTECTED] Subject: Re: [R] help with nls and Hill equation Hi! I would suggest trying out a few different starting values as

Re: [R] help with nls and Hill equation

Thanks. I am just not used to having such a huge difference when changing the initial condition by 1 point. it usually tends to be an issue when you are way off (especially since the hill converged at 1.69). Does it have something to do with the algorithm or is the hill just very finicky? Lanre

Re: [R] help with nls and Hill equation

Hi! I would suggest trying out a few different starting values as a first unsystematic approach. For example changing hill=1 to hill=2 results in convergence: foo.nls<-nls(var~Emax*(Dose^hill)/((EC50^hill)+(Dose^hill)), start=list(Emax=-4,EC50=269,hill=2),trace=T,data=foo) Christian ___

[R] help with nls and Hill equation

Hello all, I am having a problem with nls. I have such data as shown below, foo<- Dosevar 0 0.00 100 -1.318178 200 -1.562425 400 -3.579960 1200 -3.788662 however, when I call nls as shown below, >foo.nls<-nls(var~Emax*(Dose^hill)/((EC50^hill)+(Dose^hill)), + start