nls problem with R
The fact that T2 and V2 are of different lengths seems like a likely culprit. Other than that, you need to find start points that do not lead to a singular gradient. There are several books that provide advice on obtaining initial parameter estimates for non-linear models. Google Books might help you. Cheers Andrew
On Tue, May 03, 2011 at 09:08:03PM -0700, sterlesser wrote:
the original data are V2 =c(371000,285000 ,156000, 20600, 4420, 3870, 5500 ) T2=c( 0.3403 ,0.4181 ,0.4986 ,0.7451 ,1.0069 ,1.553) nls2=nls(V2~v0*(1-epi+epi*exp(-cl*(T2-t0))),start=list(v0=10^7,epi=0.9,cl=6.2,t0=8.7)) after execution error occurs as below ################################################################ Error in nlsModel(formula, mf, start, wts) : singular gradient matrix at initial parameter estimates Error in nlsModel(formula, mf, start, wts) : singular gradient matrix at initial parameter estimates In addition: Warning messages: 1: In lhs - rhs : longer object length is not a multiple of shorter object length 2: In .swts * attr(rhs, "gradient") : longer object length is not a multiple of shorter object length could anyone help me ?thansks -- View this message in context: http://r.789695.n4.nabble.com/nls-problem-with-R-tp3494454p3494454.html Sent from the R help mailing list archive at Nabble.com.
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