On Tue, Aug 07, 2012 at 11:59:09PM +0100, Mat Jaggard wrote:
> I have tried to create a polynomial that fits some data using the
> following code:
>
> PolynomialFitter fitter = new PolynomialFitter(14, new
> GaussNewtonOptimizer());
> for (int i = 0; i < numValues; i++)
> {
> fitter.addObservedPoint(xValues[i], yValues[i]);
> }
> return new PolynomialFunction(fitter.fit());
>
> I've also tried using a degree of 4. In both cases and using both a
> GaussNewtonOptimizer and a LevenbergMarquardtOptimizer, I'm able to
> get a straight line to be fitted correctly, but the following data
> results with a constant value but very small multipliers for x, and
> higher orders.
>
> Is anyone able to let me know why this is happening and what I can do about
> it?
>
> Many thanks,
> Mat.
>
> The result I get is...
> y = 110.281064 + 0.002316943x - 3.86E-09x^2 + 4.01E-15x^3 - 1.58E-21x^4
>
> From this data:
>
> [...]
Plotting those data, and the above polynomial shows that Commons Math did a
decent job. What led you to think that the fit is not correct?
[Maybe the data could be better fitted with another function...]
Regards,
Gilles
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