"in non linear modelling finding appropriate starting values is something like an art"... (maybe from somewhere in Crawley , 2007) Here a colleague and I just want to compare different response models to a null model. This has worked OK for almost all the other data sets except that one (dumped below). Whatever our trials and algorithms, even subsetting data (to check if some singular point was the cause of the mess), we do not reach convergence... or screw up with singular gradients (?) etc...
eg: nls(pourcma~SSlogis(transat, Asym, xmid, scal), start=c(Asym=30, xmid=0.07, scal=0.02),data=bdd, weights=sqrt(nbfeces),trace=T,alg="plinear") As anyone a hint about an alternate approach to fit a model ? Or an idea to get evidence that such model cannot be fitted to the data.... bdd <- structure(list(transat = c(0.0697, 0.13079, 0.314265, 0.241613, 0.039319, 0, 0, 0, 0, 0, 0.0805, 0.41, 0.30585, 0.27465, 0.06085, 0.09114, 0.05766, 0.036983, 0.093186, 0.046624, 0, 0, 0, 0, 0.000616, 0, 0.0025, 0.0325, 0.03125, 0.04599, 0.38398, 0.524505, 0.450337, 0.061831, 0.133926, 0.091806, 0.00928, 0.25114, 0.3074, 0.431056, 0.026158), transma = c(0.04141, 0.01599, 0.101803, 0.002378, 0.039319, 0.00472459016393443, 0.0031016393442623, 0.000178524590163934, 0.00255704918032787, 0.000346229508196721, 0.0665, 0.012, 0.0553, 0.0045, 0.0056, 0.00155, 0.00124, 0.011966, 0.001736, 0.004712, 3.62903225806452e-05, 9.79838709677419e-05, 2.20161290322581e-05, 0.00462, 0.0100644444444444, 0.00213111111111111, 0.046, 0.005, 0.01195, 0.07154, 0.08468, 0.141182, 0.086578, 0.027959, 0.003159, 0.003081, 0.13862, 0.00754, 0.078648, 0.068324, 0.025288), nbfeces = c(22L, 26L, 43L, 30L, 35L, 25L, 21L, 36L, 34L, 37L, 23L, 32L, 40L, 35L, 30L, 16L, 25L, 37L, 37L, 34L, 31L, 35L, 41L, 31L, 34L, 39L, 5L, 14L, 31L, 13L, 21L, 34L, 32L, 36L, 36L, 40L, 31L, 35L, 39L, 29L, 32L), pourcma = c(50, 34.6153846153846, 27.9069767441860, 43.3333333333333, 65.7142857142857, 32, 28.5714285714286, 22.2222222222222, 50, 10.8108108108108, 26.0869565217391, 40.625, 12.5, 22.8571428571429, 43.3333333333333, 6.25, 4, 10.8108108108108, 16.2162162162162, 23.5294117647059, 25.8064516129032, 45.7142857142857, 39.0243902439024, 25.8064516129032, 41.6666666666667, 27.5, 20, 14.2857142857143, 22.5806451612903, 15.3846153846154, 38.0952380952381, 17.6470588235294, 78.125, 61.1111111111111, 25, 37.5, 22.5806451612903, 40, 17.9487179487179, 41.3793103448276, 50), pourcat = c(22.7272727272727, 30.7692307692308, 41.8604651162791, 56.6666666666667, 5.71428571428571, 0, 0, 0, 0, 0, 30.4347826086957, 15.625, 45, 74.2857142857143, 13.3333333333333, 50, 12, 18.9189189189189, 27.0270270270270, 20.5882352941176, 0, 0, 0, 0, 0, 5, 40, 0, 0, 7.69230769230769, 9.52380952380952, 38.2352941176471, 59.375, 5.55555555555556, 41.6666666666667, 42.5, 9.67741935483871, 14.2857142857143, 51.2820512820513, 79.3103448275862, 6.25)), .Names = c("transat", "transma", "nbfeces", "pourcma", "pourcat"), class = "data.frame", row.names = c(NA, -41L)) ______________________________________________ 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.