Welcome to the wonderful world Of nonlinear model fitting in ill-conditioned problems. See also chaos theory.
Bert Sent from my iPhone -- please excuse typos. On Apr 3, 2012, at 3:03 PM, Ramiro Barrantes <[email protected]> wrote: > Hello, > > I am using CentOS Linux 6.0, R 2.14.1 and nlme 3.1-103 > > I am trying to fit some models using nlme, and what was happening was that it > would get to some datasets and just "stall", the memory usage would grow and > grow and eventually crash. > > I looked carefully into one of the datasets and ran it separately. It worked. > After narrowing down on all possibilities, I found that the main difference > between both was in the initial values. If one subtracts them: > >> initialValuesOriginal - initialValuesThatWorks > A.R A.a A.y B.R B.a > -3.194922e-08 0.000000e+00 0.000000e+00 -9.249630e-08 0.000000e+00 > B.y C.R C.a C.y D.R > 0.000000e+00 -1.713935e-06 -8.639821e-09 1.032083e-09 3.716880e-08 > D.a D.y E.R E.a E.y > 0.000000e+00 0.000000e+00 1.766460e-06 0.000000e+00 0.000000e+00 > > How come such a small difference can have such a big effect? (working ok, > versus stalling the entire computer) > > I also just played with rounding to 10 decimal digits and it worked fine. > > I will look into what nlme is doing tomorrow, but was wondering if perhaps > there is something that I don't know about how R works, or using numbers with > many decimals in nlme for initial values, that would create such a phenomenon. > > Thanks in advance, > Ramiro > > [[alternative HTML version deleted]] > > ______________________________________________ > [email protected] 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. ______________________________________________ [email protected] 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.
