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 [EMAIL PROTECTED] http://www.uni-kiel.de/agrarpol/ahenningsen/ ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html