Subject: Re: [R] optim function Date: Fri, 13 Jul 2018 17:06:56 -0400 From: J C Nash <profjcn...@gmail.com> To: Federico Becerra <fbece...@mdp.edu.ar>
Though I wrote the original codes for 3 of the 5 solvers in optim(), I now suggest using more recent ones, some of which I have packaged. optimx on R-forge (not the one on CRAN yet) has optimr() function that has same syntax as optim but more options. See https://r-forge.r-project.org/projects/optimizer/. You need an objective function myobj(parameters, other_data) that is smaller the better the model fit. Then solution <- optimr(startparameters, myobj, method="chosen-method") will try to optimize. If you can supply a gradient function, then you will usually do much better. My book, Nonlinear Parameter Optimization Using R Tools (2014) gives quite a few examples, but doesn't have the optimr() function -- it's more recent. And do -- repeat do -- check your function VERY carefully. It is worth it. If the objective is in any way wrong, badly scaled, etc. you WILL get into trouble. John Nash On 2018-07-13 02:43 PM, Federico Becerra wrote: > Good afternoon, > > I am a Biology researcher working on Functional Morphology and Behaviour in > mammals. Nowadays, I have a series of > morphological data that I would like to test against different models for > which I would need to optimize them -namely, > "randomly manipulating" all models parameters in order to find the model that > fit best upon my data. > > I've been told that the function "optim" is THE function for me, but I've > been having problems to program it and set all > constraints. > > Is there anything you could help me (guide me) with? I've asked already > several "experts" in the internet but noone gave > me a real solution. > > Thanks a lot, have a nice day, > Federico > ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
