Try squaring both sides of the formula. On Wed, Sep 3, 2008 at 10:01 AM, Benoit Boulinguiez <[EMAIL PROTECTED]> 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/ > > > > [[alternative HTML version deleted]] > > > ______________________________________________ > 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.
