Re: [R] Logistic regression

From: Guillaume Brutel <guillaume.brutel_at_yahoo.fr>
Date: Tue, 15 Apr 2008 10:29:15 +0200


>
> >/ I am trying to fit a non linear regression model to time series data.
> />/
> />/ If I do this:
> />/ reg.logis = nls(myVar~SSlogis(myTime,Asym,xmid,scal))
> />/ I get this error message (translated to English from French):
> />/ Erreur in nls(y ~ 1/(1 + exp((xmid - x)/scal)), data = xy, start =
> />/ list(xmid = aux[1], :
> />/ le pas 0.000488281 became inferior to 'minFactor' of 0.000976562
> /
> If it occurs after a few iterations (was it verbose=TRUE; sorry, no docs at
> hand), almost always means that there is no unique solution. Are you sure that
> your data level out at 1? Or is a normalization factor needed? Try to repost
> with the original data set if possible. This error message might also turn up
> when the start values were totally off, so try to plot the curve and the data
> with the start values.
>
> Setting minFactor never helped for me in that case.
>
> Dieter
Here is the original dataset I am working on:

 > myTime
Time Series:
Start = 0
End = 1066
Frequency = 0.0769230769230769
 [1] 0 13 26 39 52 65 78 91 104 117 130 143 156 169 182
[16] 195 208 221 234 247 260 273 286 299 312 325 338 351 364 377
[31] 390 403 416 429 442 455 468 481 494 507 520 533 546 559 572
[46] 585 598 611 624 637 650 663 676 689 702 715 728 741 754 767
[61] 780 793 806 819 832 845 858 871 884 897 910 923 936 949 962
[76] 975 988 1001 1014 1027 1040 1053 1066  >
 > myVar
Time Series:
Start = 0
End = 1066
Frequency = 0.0769230769230769

 [1]  59.88812  60.32571  60.76331  61.20090  61.63849  58.63085  59.25744
 [8]  71.99815  54.14649  25.11732  52.28806  47.93601  38.20542  43.55031
[15] 101.35488  90.63455  79.91422  69.19390  58.47357  41.52232  48.24774
[22]  31.24054  32.98928  35.33158  15.96929  17.73995  19.65816  21.57638
[29]  23.49459  26.14397  28.92629  31.70861  35.75325  46.74069  57.72812
[36]  69.56075  41.51180  27.91007  41.16375  51.24584  60.75127  70.25670
[43]  27.28310  28.82234  30.36158  31.90082  33.44006  34.97930  36.51854
[50]  75.18015  39.08242  53.25049  21.68338  21.72782  24.50556  29.30659
[57]  27.59313  23.92532  20.25751  16.30756  49.36701  87.93636  32.38620
[64]  28.05113  23.89006  27.63523  24.84287  23.81066  35.87769  24.84182
[71]  28.53371  19.53002  13.27322  15.30672  17.34021  29.75360  19.13744
[78]  29.09236  27.75517  26.52083  19.98650  26.09178  54.22785
 >

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