# [R] Help specifying a non-linear model in nlsLM()

Bert Gunter gunter.berton at gene.com
Tue Dec 16 17:24:45 CET 2014

```Suitable help may not be possible. I suspect that either your
function/code is funky (is the function smooth, non-infinite near your
starting value?) or you are overparameterized. If the latter, the
remedy may depend on the nature of your data, which you have not
shared.

While you may receive some help here (there are some pretty smart
optimizers who monitor the list), I suggest you try a statistical site
like stats.stackexchange.com for help, as this appears to be primarily
a statistics issue, not an R programming one.

Cheers,
Bert

Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
Clifford Stoll

On Tue, Dec 16, 2014 at 6:26 AM, Chandrasekhar Rudrappa
<chandratr at gmail.com> wrote:
> Dear All,
>
> I am trying to fit the following model in nlsLM():
>
> fn5 <- function(x, T, t1, w_inf, Lt0){
> S<-function(x, T, t1){
> x+(1-T)/(2*pi)*sin(2*pi*(x-t1)/(1-T))
> }
> F <- function(x, T, t1){
> t2 <- t1 + (1-T)/2
> t3 <- t1 + (1+T)/2
> t.factorial <- x%%1
> floor(x)*(1-T) + S(t.factorial, T, t1)*(0<=t.factorial & t.factorial<t2) +
> S(t2, T, t1)*(t2<=t.factorial & t.factorial<t3) +
> S(t.factorial-T, T, t1)*(t3<=t.factorial & t.factorial<1)
> }
> return(w_inf - (w_inf - Lt0)*exp(-(2/30)*(F(x,T,t1)-F(7,T,t1))))
> }
> fn6<- y~fn5(x, T, t1, w_inf, Lt0)
> startval<-c(x=x, T=0.035, t1=0.359, w_inf=135, Lt0=47)
> (nlsktm1 <- nlsLM(fn6, start=startval, lower=c(x=x, T=0.0135, t1=0.259,
> w_inf=131, Lt0=41), jac=NULL, trace=T, data=ktm,
> control=nls.control(maxiter=10)))
>
> When I run the above script, the following error is displayed:
>
> Error in nlsModel(formula, mf, start, wts) :
>   singular gradient matrix at initial parameter estimates
> In nls.lm(par = start, fn = FCT, jac = jac, control = control, lower =
> lower,  :
>   lmdif: info = 0. Improper input parameters.
>
> Suitable help is requested.
> --
> Dr. TR Chandrasekhar, M.Sc., M. Tech., Ph. D.,
> Sr. Scientist
> Rubber Research Institute of India
> Hevea Breeding Sub Station
> DK Dt., Karnataka
> Phone-Land: 08251-214336
> Mobile: 9448780118
>
>         [[alternative HTML version deleted]]
>
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