[R] help with nls and Hill equation

[Lanre Okusanya]

Hello all, I am having a problem with nls. I have such data as shown below,
foo<-
Dose    var
0      0.000000
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=list(Emax=-4,EC50=269,hill=1),trace=T,data=foo)

i get the response below.

      1.759088 :   -4 269   1
    Error in numericDeriv(form[[3]], names(ind), env) :
     Missing value or an infinity produced when evaluating the model


if i remove the hill variable, it works. can someone help me out with
what I am coding wrong.

Thanks,



Lanre