Constrained non linear regression using ML
Dear R users, I have to fit the non linear regression: y~1-exp(-(k0+k1*p1+k2*p2+ .... +kn*pn)) where ki>=0 for each i in [1 .... n] and pi are on R+. I am using, at the moment, nls, but I would rather use a Maximum Likelhood based algorithm. The error is not necessarily normally distributed. y is approximately beta distributed, and the volume of data is medium to large (the y,pi may have ~ 40,000 elements). I have studied the packages in the task views Optimisation and Robust Statistical Methods, but I did look like what I was looking for was there. Maybe I am wrong. The nearest thing was nlrob, but even that does not allow for constraints, as far as I can understand. Any suggestion? Regards
Corrado Topi PhD Researcher Global Climate Change and Biodiversity Area 18,Department of Biology University of York, York, YO10 5YW, UK Phone: + 44 (0) 1904 328645, E-mail: ct529 at york.ac.uk