[R] nonlinear regression and Excel solver

[Arne Henningsen]

Hi,

I don't know S-Plus and its functions nlminb() and ms(). However, in R I would 
use optim(), optimize or nlm(). I used these functions quiet often and had 
only very few problems. I think that R is better, easier and more flexible 
than Excel (at least in the long run), but since I don't anything about the 
Lefkovitch matrix framework I might be wrong in this case.

Best wishes,
Arne

On Wednesday 14 January 2004 19:57, Kristian Omland wrote:
> Hi all,
>
> Earlier today I posted this question on s-news, so apologies to some for
> the duplication.
>
> > Please put aside your snobbery about Microsoft products for a moment.
> >
> > I am fitting population models to annual survey data for trout. For those
> > of you familiar with ecological models, I am working in the Lefkovitch
> > matrix framework; for those unfamiliar with that shorthand, the modeled
> > variable is a vector of abundances of fish in five size classes, with a
> > system of linear equations (represented by a matrix) governing survival,
> > advancement from smaller to larger stages, and reproduction.
> >
> > So far, I have been using a likelihood approach in an Excel spreadsheet.
> > The spreadsheet includes the annual survey data, the Lefkovitch matrix,
> > and projections of the model, i.e., realizations to be compared to the
> > data. It computes the negative log-likelihood of each realization
> > assuming log-normally distributed noise and the sum of those likelihood
> > components. I use the Solver add-in to minimize the negative
> > log-likelihood over the parameters in the Lefkovitch matrix.
> >
> > I have made a tentative stab at using nlminb() [minor success] and ms()
> > [no success] to fit the model in S-Plus, but my proficiency is such that
> > I still have greater flexibility fitting the models with Excel. Thus my
> > question for you all is ...
> >
> > Is Excel’s Solver an adequate tool for numerical approximation in general
> > and nonlinear regression in particular? Or should I push on writing
> > S-Plus code?
> >
> > Is anyone out there interested in assisting me with S-Plus code with the
> > potential payoff of collaboration on a publication in the ecological
> > literature?
>
> Obviously, I would be equally enthused if an R user was interested in a
> collaboration.
>
> Thanks in advance,
> Kristian

-- 
Arne Henningsen
Department of Agricultural Economics
University of Kiel
Olshausenstr. 40
D-24098 Kiel (Germany)
Tel: +49-431-880 4445
Fax: +49-431-880 1397
ahenningsen at agric-econ.uni-kiel.de
http://www.uni-kiel.de/agrarpol/ahenningsen/