Had this to calculate the rsquared:
OLSMultipleLinearRegression regression = new OLSMultipleLinearRegression();
regression.newSampleData(curve_totals, data);
System.out.println("rsquared:" + regression.calculateRSquared());
Where curve_totals is the value calculated with Fnc.fnc and the calculated a, b and c.
Used this as reference: http://commons.apache.org/math/userguide/stat.html
Is that right?
By the way, there is a typo in the link: double rSquared = regression.caclulateRSquared();
Where could I report it?
> Date: Sat, 7 Jul 2012 00:29:51 +0200
> From: gilles@harfang.homelinux.org
> To: user@commons.apache.org
> Subject: Re: [math]
>
> On Fri, Jul 06, 2012 at 09:39:30PM +0000, Italo Maia wrote:
> >
> > Hummm, so my assumption that my previous values for a, b and c were the best are
wrong. I calculated the resid and it is really smaller. Real thanks for that!
>
> I wouldn't take the difference too seriously, given that the data are not
> really close to the curve. The errors seem quite large.
>
> > Any tips on calculating the rsquared?
>
> No.
>
> Gilles
>
> >
> > Date: Fri, 6 Jul 2012 22:05:26 +0200
> > From: gilles@harfang.homelinux.org
> > To: user@commons.apache.org
> > Subject: Re: [math]
> >
> > Hi.
> >
> > If you are using the function
> >
> > a * Math.pow(t, b) * Math.exp(c * t)
> >
> > the gradient is:
> >
> > { Math.pow(t, b) * Math.exp(c * t),
> > a * Math.log(t) * Math.pow(t, b) * Math.exp(c * t),
> > a * t Math.pow(t, b) * Math.exp(c * t) }
> >
> > > // No idea what goes here. Nothing seems to work.
> >
> > Well, the gradient (partial derivatives w.r.t the parameters) is the thing
> > that will work; the attached figure shows the data and the function that
> > fits it with
> > a = 1.097378664278161
> > b = 0.4273818336149512
> > c = 0.01457006142420487
> >
> > >
> > > a, b and c for this example should be: A: 1.0782 B: 0.4583 C: 0.0166
> >
> > The fit is slightly better with the values found by "CurveFitter"
> > (the "LevenbergMarquardt" algorithm actually).
> >
> > Regards,
> > Gilles
> >
> >
> > 
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