R help - Jun 2011 - Error in NLS example in the documentation

Hello there,

I am trying to use R function NLS to analyze my data and one of the examples
in the documentation is -

## the nls() internal cheap guess for starting values can be sufficient:

x <- -(1:100)/10
y <- 100 + 10 * exp(x / 2) + rnorm(x)/10
nlmod <- nls(y ~  Const + A * exp(B * x), trace=TRUE)

plot(x,y, main = "nls(*), data, true function and fit, n=100")
curve(100 + 10 * exp(x / 2), col=4, add = TRUE)
lines(x, predict(nlmod), col=2)

However, when I try to execute this - I get the following error-

Error in nls(y ~ Const + A * exp(B * x), trace = TRUE) :
  step factor 0.000488281 reduced below 'minFactor' of 0.000976562
In addition: Warning message:
In nls(y ~ Const + A * exp(B * x), trace = TRUE) :
  No starting values specified for some parameters

Can someone propose how I can fix this error? Thanks.

Diviya

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On Jun 12, 2011, at 20:25 , Diviya Smith wrote:
> Hello there,
> 
> I am trying to use R function NLS to analyze my data and one of the
examples
> in the documentation is -
> 
> ## the nls() internal cheap guess for starting values can be sufficient:
> 
> x <- -(1:100)/10
> y <- 100 + 10 * exp(x / 2) + rnorm(x)/10
> nlmod <- nls(y ~  Const + A * exp(B * x), trace=TRUE)
> 
> plot(x,y, main = "nls(*), data, true function and fit, n=100")
> curve(100 + 10 * exp(x / 2), col=4, add = TRUE)
> lines(x, predict(nlmod), col=2)
> 
> However, when I try to execute this - I get the following error-
> 
> Error in nls(y ~ Const + A * exp(B * x), trace = TRUE) :
>  step factor 0.000488281 reduced below 'minFactor' of 0.000976562
> In addition: Warning message:
> In nls(y ~ Const + A * exp(B * x), trace = TRUE) :
>  No starting values specified for some parameters
> 
> Can someone propose how I can fix this error? Thanks.
Works for me. However, if you predefine some of the parameters, all bets are
off, e.g.

B <- 1000
example(nls)


Try again with a clean workspace. 

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com