I think you need to consult a local statistician, as you appear to be so far out of your depth statistically that even the best-intentioned help from this list may not suffice. For example, if I were that local statistician, I would ask: what is the context? -- what is the underlying scientific issue that led to this model? -- what are the data? -- etc. etc. before I would even hazard advice on the statistical details(Please do not answer these questions either publicly or privately, as they are just fyi's).
Bert Gunter Genentech Nonclinical Biostatisics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Lindsay Banin Sent: Tuesday, August 25, 2009 9:02 AM To: 'r-help@r-project.org' Subject: [R] Covariates in NLS (Multiple nonlinear regression) Dear R-users, I am trying to create a model using the NLS function, such that: Y = f(X) + q + e Where f is a nonlinear (Weibull: a*(1-exp(-b*X^c)) function of X and q is a covariate (continous variable) and e is an error term. I know that you can create multiple nonlinear regressions where x is polynomial for example, but is it possible to do this kind of thing when x is a function with unknown coefficients (a,b,c)? Ultimately, I am expecting the output to give individual regression models for each coefficient (a,b,c) with q as a covariate. I have tried the following code, and get the resultant error messages: > weib.nls <- nls(Y ~ (a*(1-exp(-b*X^c)))|q, > + data=DATA, > + start=c(a=75,b=0.05,c=0.7)) > Error in nlsModel(formula, mf, start, wts) : > singular gradient matrix at initial parameter estimates > > summary(weib.nls) > > weib.nls2 <- nls(Y~ (a*(1-exp(-b*X^c)))+q, > + data=DATA, > + start=c(a=75,b=0.05,c=0.7)) > Error in numericDeriv(form[[3L]], names(ind), env) : > Missing value or an infinity produced when evaluating the model > Many thanks in advance! Lindsay ______________________________________________ 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. ______________________________________________ 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.