To add to Gabor's remarks: This has nothing to do per se with R -- it is your insufficient understanding of the underlying mathematical issues.
It is pretty trivial to do the plinear algorithm by hand. Fit linear regressions weight ~ lm(weight ~z) where z is exp(gamma*week) for a suitable sequence of gamma values and just choose that which gives the best fit. Or use this to get a starting value for nls. -- Bert On Thu, Jul 12, 2012 at 1:03 PM, Gabor Grothendieck <ggrothendi...@gmail.com > wrote: > On Thu, Jul 12, 2012 at 3:40 PM, Felipe Carrillo > <mazatlanmex...@yahoo.com> wrote: > > I get a different error now: > >> nls(weight ~ cbind(1, exp(gamma*week)), weightData, start = list(gamma= > >> 0.2), alg = "plinear") > > Error in nls(weight ~ cbind(1, exp(gamma * week)), weightData, start = > > list(gamma = 0.2), : > > step factor 0.000488281 reduced below 'minFactor' of 0.000976562 > > The help file says: ........When start is missing, a very cheap guess for > > start is tried (if algorithm != "plinear"). > > > Please give a reproducible example by setting the seed. This > reproducible example converges: > > > set.seed(123) > > weight_random <- runif(50,1,24) > > weight <- sort(weight_random) > > weightData <- data.frame(weight,week=1:50) > > nls(weight ~ cbind(1, exp(gamma*week)), weightData, start = list(gamma = > 0.2), alg = "plinear") > Nonlinear regression model > model: weight ~ cbind(1, exp(gamma * week)) > data: weightData > gamma .lin1 .lin2 > 1.136e-03 -3.949e+02 3.962e+02 > residual sum-of-squares: 9.17 > > Number of iterations to convergence: 8 > Achieved convergence tolerance: 9.581e-06 > > as does nls with Gauss Newton: > > > nls(weight ~ alpha + beta*exp(gamma*week), weightData, start = > + c(alpha = 0.0, beta = 1, gamma = 0.2) > + ) > Nonlinear regression model > model: weight ~ alpha + beta * exp(gamma * week) > data: weightData > alpha beta gamma > -3.949e+02 3.961e+02 1.136e-03 > residual sum-of-squares: 9.17 > > Number of iterations to convergence: 48 > Achieved convergence tolerance: 2.906e-06 > > > > > So I removed 'plinear' from the call and got the following: > > nls(weight ~ cbind(1, exp(gamma*week)), weightData,start = > > list(gamma=0.2),trace=TRUE) > > It cannot be specified as if it were a plinear model but then use > Gauss-Newton. See ?nls > > > -- > Statistics & Software Consulting > GKX Group, GKX Associates Inc. > tel: 1-877-GKX-GROUP > email: ggrothendieck at gmail.com > > ______________________________________________ > R-help@r-project.org mailing list > 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. > -- Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list 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.
