On Mon, April 30, 2012 13:10, Jeremy Sanders wrote: > On 28/04/12 11:48, Antonio wrote: >> Hello everybody, >> I checked Veusz linear fit against a certified data set coming from NIST: >> Statistical Reference Datasets http://www.itl.nist.gov/div898/strd/ . >> In particular, the first one I used was the Norris dataset you could find >> here: >> http://www.itl.nist.gov/div898/strd/lls/data/Norris.shtml . >> Maybe I did something weird and stupid but the line fit does not look like >> the >> data plot and coefficients are pretty different from certified ones. >> >> I checked the dataset against gnuplot, gnumeric, extrema, labplot, SSP, PSPP, >> ... and the fit looks allright with them. > > Thanks - I didn't get the line to fit initially, but that appears to be > because it doesn't have any uncertainties associated with it. Veusz > assumes 5% errors if there are no uncertainties, which doesn't work in > some cases with the minimisation procedure. Probably because the 5% > errors give lots of weight to the values near zero. I haven't tested > whether pyminuit does a better job (veusz supports this as an optional > fitting module).
I loaded your test.vsz in a pyminuit build and get similar results to you: the fit is very strange if I include the points near zero with relative error bars, but works fine using either the fixed uncertainties data set or if I just exclude the points with x < 1. So I agree that this is indeed related to the default assumed 5% uncertainty. Regards, -- BKS _______________________________________________ Veusz-discuss mailing list Veusz-discuss@gna.org https://mail.gna.org/listinfo/veusz-discuss
