On Wed, 24 Oct 2007, Rafael Barros de Rezende wrote:
>
> Error in model.frame
>
> When I run the following nls model an error message appears and I dont
> know how to solve that. Could you help me??
>
> mat = c(1,2,3,4,5,6,7,8,9,12,16,24,36,48,60)
>
> for (i in 1:length(j30)) {
> bliss = nls(c(j[i,1:length(mat)]) ~ b0 + b1*((1-exp(-k1*mat))/(k1*mat)) +
> b2*(((1-exp(-k2*mat))/(k2*mat))-exp(-k2*mat)),
> start = list(k1=0.1993, k2=0.1993, b0= 22.0046, b1=-2.7661, b2=-5.8912),
> trace = TRUE)
> }
>
> Error in model.frame(formula, rownames, variables, varnames, extras,
> extranames, :
> variable lengths differ (found in 'mat')
>
> j is a (1883 x 15) matrix so I have 1883 nls regressions of j lines on mat
> as we can see in model bliss.
>
> The traceback() shows the following:
>
> > traceback()
> 6: model.frame.default(formula = ~j + mat)
> 5: model.frame(formula = ~j + mat)
> 4: eval(expr, envir, enclos)
> 3: eval(expr, p)
> 2: eval.parent(mf)
> 1: nls(c(j[i, 1:length(mat)]) ~ b0 + b1 * ((1 - exp(-k1 * mat))/(k1 *
> mat)) + b2 * (((1 - exp(-k2 * mat))/(k2 * mat)) - exp(-k2 *
> mat)), start = list(k1 = 0.1993, k2 = 0.1993, b0 = 22.0046,
> b1 = -2.7661, b2 = -5.8912), trace = TRUE)
>
> It seems that the error is in 6: model.frame.default(formula = ~j + mat) or
> 5: model.frame(formula = ~j + mat), cause the formula should be (formula = j
> ~ mat).
No, nls uses a one-sided formula to get the model frame. The error is
that 'mat' and 'j' are not of the same length. You can't use
c(j[i,1:length(mat)]) in an nls formula: assign it to a variable and use
that instead.
> Am I right about that?? Again, how could I fix this problem?? I need a help
> here...
>
> Thanks.
> Rafael Barros de Rezende
> Economics MPhill Candidate - Curriculum Lattes:
> [1]http://lattes.cnpq.br/9826095609825249
> Cedeplar - Development and Regional Planning Center
> Face, UFMG ([2]http://www.cedeplar.ufmg.br) - Brazil
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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