[R] nls convergence trouble

[Gabor Grothendieck]

Try squaring both sides of the formula.

On Wed, Sep 3, 2008 at 10:01 AM, Benoit Boulinguiez
<benoit.boulinguiez at ensc-rennes.fr> wrote:
> Hi,
>
> Parameters assessment in R with nls doesn't work, though it works fine with
> MS Excel with the internal solver :(
>
>
> I use nls in R to determine two parameters (a,b) from experimental data.
>
>        m         V        C0         Ce        Qe
> 1  0.0911 0.0021740  3987.581   27.11637  94.51206
> 2  0.0911 0.0021740  3987.581   27.41915  94.50484
> 3  0.0911 0.0021740  3987.581   27.89362  94.49352
> 4  0.0906 0.0021740  5981.370   82.98477 189.37739
> 5  0.0906 0.0021740  5981.370   84.46435 189.34188
> 6  0.0906 0.0021740  5981.370   85.33213 189.32106
> 7  0.0911 0.0021740  7975.161  192.54276 233.30310
> 8  0.0911 0.0021740  7975.161  196.52891 233.20797
> 9  0.0911 0.0021740  7975.161  203.07467 233.05176
> 10 0.0906 0.0021872  9968.951  357.49157 328.29824
> 11 0.0906 0.0021872  9968.951  368.47609 328.03306
> 12 0.0906 0.0021872  9968.951  379.18904 327.77444
> 13 0.0904 0.0021740 13956.532 1382.61955 350.33391
> 14 0.0904 0.0021740 13956.532 1389.64915 350.16485
> 15 0.0904 0.0021740 13956.532 1411.87726 349.63030
> 16 0.0902 0.0021740 15950.322 2592.90486 367.38460
> 17 0.0902 0.0021740 15950.322 2606.34599 367.06064
> 18 0.0902 0.0021740 15950.322 2639.54301 366.26053
> 19 0.0906 0.0021872 17835.817 3894.12224 336.57036
> 20 0.0906 0.0021872 17835.817 3950.35273 335.21289
> 21 0.0906 0.0021872 17835.817 3972.29367 334.68320
>
> the model "LgmAltformula" is
>
> Qe ~ (V + b * m * a + C0 * V * b - ((C0 * V * b)^2 + 2 * C0 *
>    b * V^2 - 2 * C0 * V * m * a * b^2 + V^2 + 2 * V * m * a *
>    b + (b * m * a)^2)^(1/2))/(2 * b * m)
>
> the command in R is
>
>
> nls(formula=LgmAltFormula,data=bois.DATA,start=list(a=300,b=0.01),trace=TRUE
> ,control=nls.control(minFactor=0.000000009))
>
> R has difficulties to converge and stops after the maximum of iterations
>
> 64650.47 :  2.945876e+02 3.837609e+08
> 64650.45 :  2.945876e+02 4.022722e+09
> 64650.45 :  2.945876e+02 1.695669e+09
> 64650.45 :  2.945876e+02 5.103971e+08
> 64650.44 :  2.945876e+02 8.497431e+08
> 64650.41 :  2.945876e+02 1.515243e+09
> 64650.36 :  2.945877e+02 5.482744e+09
> 64650.36 :  2.945877e+02 2.152294e+09
> 64650.36 :  2.945877e+02 7.953167e+08
> 64650.35 :  2.945877e+02 7.625555e+07
> Erreur dans nls(formula = LgmAltFormula, data = bois.DATA, start = list(a =
> 300,  :
>  le nombre d'itérations a dépassé le maximum de 50
>
>
> The parameters "a" and "b" are estimated to be 364 and 0.0126 with Excel
> with the same data set.
> I tried with the algorithm="port" with under and upper limits. One of the
> parameter reaches the limit and the regression stops.
>
> How can I succeed with R to make this regression?
>
>
> Regards/Cordialement
>
> -------------
> Benoit Boulinguiez
> Ph.D
> Ecole de Chimie de Rennes (ENSCR) Bureau 1.20
> Equipe CIP UMR CNRS 6226 "Sciences Chimiques de Rennes"
> Campus de Beaulieu, 263 Avenue du Général Leclerc
> 35700 Rennes, France
> Tel 33 (0)2 23 23 80 83
> Fax 33 (0)2 23 23 81 20
> http://www.ensc-rennes.fr/
>
>
>
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