Hi,
I am a non-expert user of R. I am essaying the fit of two different functions
to my data, but I receive two different error messages. I suppose I have two
different problems here... But, of which nature? In the first instance I did
try with some different starting values for the parameters, but without
success.
If anyone could suggest a sensible way to proceed to solve these I would be
really thankful!
Daniela
***
Details on data and formulas:
polcurve=read.table(polcurve.txt,header=TRUE)
polcurve
distfath
1 1 0.138908965
2 2 0.113768871
3 3 0.114361753
4 4 0.051065765
5 5 0.095787946
6 6 0.123601131
7 7 0.117340746
8 8 0.054049434
9 9 0.112000962
10 10 0.074843028
11 11 0.064735196
12 12 0.098210497
13 13 0.093786895
14 14 0.033752379
15 15 0.038961039
16 16 0.023048216
17 17 0.010018243
18 18 0.007177034
19 19 0.003787879
20 20 0.0
21 21 0.0
#Exponential power function
s=nls(fath~((b^2)/(a^2))*exp((-dist/a)^b),polcurve)
Error in numericDeriv(form[[3]], names(ind), env) :
Missing value or an infinity produced when evaluating the model
In addition: Warning message:
No starting values specified for some parameters.
Intializing 'b', 'a' to '1.'.
Consider specifying 'start' or using a selfStart model in: nls(fath ~
((b^2)/(a^2)) * exp((-dist/a)^b), polcurve)
#Geometric function
s=nls(fath~((b-1)*(b-2)/a)*((1+dist/a)^-b),polcurve)
Error in nlsModel(formula, mf, start, wts) :
singular gradient matrix at initial parameter estimates
In addition: Warning message:
No starting values specified for some parameters.
Intializing 'b', 'a' to '1.'.
Consider specifying 'start' or using a selfStart model in: nls(fath ~ ((b - 1)
* (b - 2)/a) * ((1 + dist/a)^-b),
Daniela Salvini
Ph.D. student
University of Copenhagen,
Faculty of Life Sciences,
Centre for Forest and Landscape
Hørsholm Kongevej 11
2970 Hørsholm, Denmark
e-mail: [EMAIL PROTECTED]
Tel.: (+45)35281639 / 35281645
Fax.: (+45)35281517
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