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| polynomialfit bug? http://forum.alglib.net/viewtopic.php?f=2&t=135 |
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| Author: | rbryce [ Mon Dec 06, 2010 7:31 pm ] |
| Post subject: | polynomialfit bug? |
Hi all, Great work on this code. However, I'm trying to use alglib.polynomialfit and I'm having difficulties. Generally, it works very well. However, on some datasets, I have some issues. Some insight/help would be appreciated. I'm using C#. I call it something like: alglib.polynomialfitreport rr; double [] tm; // array of double's representing time - not equal intervals but sorted in increasing order double [] xa; // array of values representing 'x' (with error) at time tm[] int poly_degree; // always 2 or 3 or 4 int info; alglib.barycentricinterpolant xb; alglib.polynomialfit(tm, xa, polydegree, out info, out xb, out rr); When I then want to generate data, I'm calling: alglib.barycentricdiff1(xb, t, out x, out slope); Pretty standard stuff, I think. But occasionally, depending on parameter t, x will calculate to NaN, even though when you look at the dataset (via a grapher), it's a pretty simple curve between tm and xa that can easily be approximated with a 2 or 3 order polynomial equation. The value is either completely valid or NaN. I had originally tried to call polynomialbar2pow() but it always gives me unreasonable results. polynomialpow2bar(), and polynomialbar2pow() seem to reasonable duals when I first start with a polynomial, but not in these instances. My hunch is I am possibly using it incorrectly? Or possibly using the wrong routine to curve fit a polynomial through a set of points defined by (tm, xa)? Or is there a bug here? When it works 99% of the time, my gut says bug, but this is my first attempt playing with the package, too. Help would be appreciated! Thanks, --Rob |
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| Author: | Sergey.Bochkanov [ Tue Dec 07, 2010 7:21 am ] |
| Post subject: | Re: polynomialfit bug? |
Can you post code/data which builds curve, tries to calculate it and gets NAN as result? |
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| Author: | rbryce [ Tue Dec 07, 2010 11:30 pm ] |
| Post subject: | Re: polynomialfit bug? |
i will asap! |
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