[R] problem plotting curve through data

[Douglas Bates]

Christian Reilly <heron at stanford.edu> writes:

> I'm having trouble plotting a curve (basically a dose-response
> function) through a set of data.
> 
> I have created a dataframe (df) of Stimulus Intensities (xstim) and
> Normalized Responses (yresp), and I've used nls() to calculate a nonlinear
> regression, like so:
> 
> 
> --------------------
> > f <- yresp ~ xstim^n / (xstim^n + B^n)
> > starts <- list(n=.6,  B=11)
> > myfit <- nls(formula=f, data=df, start = starts)
> >myfit
> 
> Nonlinear regression model
>   model:  yresp ~ xstim^n/(xstim^n + B^n)
>    data:  df
>         n         B
> 0.8476233 5.7943791
>  residual sum-of-squares:  0.03913122
> >
> -----------
> 
> Which seems great, but I'd like to be able to plot this curve through my
> data to see how the fit looks.
> 
> when I try:
> 
> ------------
> > plot(f,data=df)
> Error in terms.formula(formula, data = data) :
> 	invalid power in formula
> ----------
> 
> or
> 
> ----------
> > n <- 0.87
> > B <- 5.7
> > plot(f,data=df)
> Error in terms.formula(formula, data = data) :
> 	invalid power in formula
> ------------

Use predict.nls to get the fitted response curve.  See
?predict.nls
and especially the example, which you can run with
example(predict.nls)