[R] using nls to fit a curve to data

[Ben Bolker]

jpl <s-jlubben1 <at> math.unl.edu> writes:

> 
> 
> Hi,
> 
> I am trying to fit a curve to data.  My command line is:
> 
>
model10=nls(offspring~((A*c^k)/gamma(k))*
 ((degdays-alpha)^(k-1))*exp(-c*(degdays-alpha)),
> 	start=list(A=30,k=2,c=.018,alpha=131))
> 

  try trace=TRUE to see where the function is trying to go.
I think you could also simplify this a bit:

model10 = nls(offspring~A*dgamma(degdays-alpha,rate=c,shape=k),...)

You can probably also use algorithm="plinear" and eliminate
the explicit A parameter.

 I would also consider using algorithm="port" and setting
lower and upper boundaries.

  good luck,
   Ben Bolker