Hi
Try
x <- -(1:100)/10
set.seed(1)
y <- 100 + 10 * exp(x / 2) + rnorm(x)/10
short cut to starting values
lm(log(y) ~-log(x+10))
Call:
lm(formula = log(y) ~ -log(x + 10))
Coefficients:
(Intercept)
4.624
nlmod <- nls(y ~ A + B * exp(C * x), start=list(A=90, B=5,C=0.1))
Formula: y ~ A + B * exp(C * x)
Parameters:
Estimate Std. Error t value Pr(>|t|)
A 100.009079 0.017797 5619.4 <2e-16
B 9.999993 0.042718 234.1 <2e-16
C 0.499529 0.004495 111.1 <2e-16
Residual standard error: 0.09073 on 97 degrees of freedom
Number of iterations to convergence: 5
Achieved convergence tolerance: 0.00000002475
I will leave you to plot the results as a check
Duncan
Duncan Mackay
Department of Agronomy and Soil Science
University of New England
Armidale NSW 2351
Email: home: mac...@northnet.com.au
At 09:16 26/04/2013, you wrote:
Content-Type: text/plain
Content-Disposition: inline
Content-length: 899
Greets,
I'm trying to learn to use nls and was running the example code for
an exponential model:
> x <- -(1:100)/10
> y <- 100 + 10 * exp(x / 2) + rnorm(x)/10
> nlmod <- nls(y ~ Const + A * exp(B * x))
Error in B * x : non-numeric argument to binary operator
In addition: Warning message:
In nls(y ~ Const + A * exp(B * x)) :
No starting values specified for some parameters.
Initializing 'Const' to '1.'.
Consider specifying 'start' or using a selfStart model
Presumably, the code should work if it is part of an example on the
help page. In perusing various help forums for similar problems, it
also appears that others believe this syntax should work in the model formula.
Any ideas?
Perhaps also, a pointer to a comprehensive and correct document that
details model formulae syntax if someone has one?
Thanks & Best Regards,
Steven
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
