[R] named list 'start' in fitdistr

[Prof Brian Ripley]

On Fri, 25 Jul 2003 vincent.stoliaroff at sgcib.com wrote:

> Hi R lovers!
> 
> I'd like to know how to use the parameter 'start' in the function
> fitdistr()

kindly provided for you in package MASS, but churlishly unattributed

> obviously I have to provide the initial value of the parameter to optimize
> except in the case of a certain set of given distribution
> 
> 
> Indeed according to the help file for fitdistr
> "     For the following named distributions, reasonable starting values
>      will be computed if `start' is omitted or only partially
>      specified: `cauchy', `gamma', `logistic', `negative binomial' (R
>      only, parametrized by `mu' and `size'), `t', `uniform', `weibull'.   "
> 
> 
> However I cannot fit an univariate distribution named 'test'

??? did you mean a distribution named `lognormal'?

> I get this:
> 
> >fitdistr(test,"lognormal")
> Error in fitdistr(test, "lognormal") : `start' must be a named list
> 
> > fitdistr(test,"lognormal",start$meanlog=0,start$sdlog=1)
> Error: syntax error
> 
> How I am supposed to type a value for start depending on the distribution
> on which I am fitting my set

On reading the help page:

   start: A named list giving the parameters to be optimized with
          initial values. 

so 

> test <- rlnorm(100, meanlog=0, sdlog=1)
> fitdistr(test, "lognormal", start=list(meanlog=0, sdlog=1))

works, just like it says it would.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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