I'm tyring to fit a relatively simple nls model to some data, but keep coming up against the same error (code follows):

Oto=nls(Otolith ~ Linf*(1-exp(-k(AGE-to))), 
    data = ages, 
    start = list(Linf=1000, k=0.1, to=0.1), 
    trace = TRUE) 

The error message I keep getting is "Error in eval(expr, envir, enclos) : could not find function "k"".  I've used this line of code for other nls models (with different data, parameter estimates, etc.), but have never gotten this error.  The data is 

AGE,Otolith,Scale
1,207.1052632,207.1052632
2,329.962963,332.7586207
3,401.9473684,406
4,422,413.1111111
5,452.6785714,458.34375
6,510.75,533
7,477,674
8,643,704
9,,615
10,695.5,
12,615,

Are the missing values (e.g., no value for Otolith, AGE 9) having an effect?  I am using Tinn-R as an editor  

I'm new to R, trying to get away from Rcmdr (though it has been helpful), and still trying to learn the language with the aid of several books on the R.  A search of the R Archive did not prove fruitful.

Thanks in advance, 

SR

Steven H. Ranney
Graduate Research Assistant (Ph.D)
USGS Montana Cooperative Fishery Research Unit
Montana State University
PO Box 173460
Bozeman, MT 59717-3460

phone: (406) 994-6643
fax:   (406) 994-7479


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