azadeh sadeghian <a.sadeghian1386 <at> yahoo.com> writes: > > I am student M.S. statistics in department statistics . I am working in the function "nls" in the [R 2.3.1]
You should update to a more recent version of R (2.6.0 is current) > with 246 data and want to fit the "exp" model to vectors( v and u ) but I > have > a problem to use it You note 246 data, but I count much less > u > 5.000000e-13 2.179057e+03 6.537171e+03 1.089529e+04 1.525340e+04 > 1.961151e+04 2.396963e+04 2.832774e+04 3.268586e+04 3.704397e+04 > 4.140209e+04 4.576020e+04 5.011831e+04 5.447643e+04 > v > 8.382562e-01 4.090868e+02 1.311053e+03 2.124143e+03 3.365494e+03 > 2.138903e+03 7.687774e+03 1.028396e+04 1.004186e+04 2.059798e+04 > 1.438464e+04 2.861373e+04 2.294919e+04 2.807701e+04 > data1<-data.frame(u=u ,v=v) > > nls(v~c0+(ce*(1-exp((-u)/ae))),data=data1,start=list(c0=0,ce=1000,ae=3000)) > Error in nls(v ~ c0 + (ce * (1 - exp((-u)/ae))), data = data1, start = list(c0 = 0, : > step factor 0.000488281 reduced below 'minFactor' of 0.000976563 To find out what was wrong, plot your data and your start value fit. You can see that the start values are far off. But, more importantly, note that you data go up exponential-like and don't level off, while you model function does. So even if you find better start values, you result may be unreasonable: how should the poor fitting function know when to bend down? This might be caused by the subset of the 246 data points you presented here. Dieter u = c( 5.000000e-13, 2.179057e+03, 6.537171e+03, 1.089529e+04, 1.525340e+04, 1.961151e+04, 2.396963e+04, 2.832774e+04, 3.268586e+04, 3.704397e+04, 4.140209e+04, 4.576020e+04, 5.011831e+04, 5.447643e+04) v = c( 8.382562e-01, 4.090868e+02, 1.311053e+03, 2.124143e+03, 3.365494e+03, 2.138903e+03, 7.687774e+03, 1.028396e+04, 1.004186e+04, 2.059798e+04, 1.438464e+04, 2.861373e+04, 2.294919e+04, 2.807701e+04) data1 = data.frame(u=u ,v=v) start=list(c0=0,ce=1000,ae=3000) v1= with(start,c0+(ce*(1-exp((-u)/ae)))) plot(u,v) lines(u,v1) v1= nls(v~c0+(ce*(1-exp((-u)/ae))),data=data1,start=start,trace=TRUE) ______________________________________________ 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.
