[R] add non-linear line

[Duncan Murdoch]

On 1/17/2007 10:42 AM, Matt Sakals wrote:
> I am trying to plot a non-linear trend line along with my data. I am  
> sure the solution is simple; any help greatly appreciated.
> 
> Recent and historic attempts:
> fit = nls((sd~a+b*exp(-c/time)+d*geology), start=list(a=1, b=1, c=10,  
> d=-1), model=TRUE)
> plot(time, sd, col=3, main = "Regression", sub=formula(fit))
> lines(time, fitted.values(fit), lwd=2)
> 
> #tt = seq(from=0, to=200, by=10)
> #lines(time, predict(fit, time=tt))
> #lines(time, predict(fit))

Your model has two independent variables, time and geology.  You won't 
get a simple trend line unless the value of geology is kept fixed.  You 
could do that with something like this code:

lines(time, predict(fit, newdata=data.frame(time=time, geology=0)))

Duncan Murdoch