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From Mat Jaggard <matt...@jaggard.org.uk>
Subject Re: [Math] Unable to fit a polynomial to data points correctly.
Date Wed, 08 Aug 2012 12:55:02 GMT
OK, I'm an idiot, please ignore this thread.

I will try to plot y = f(x) next time instead of y = f(y')

Thank you Gilles for your help.

Mat.

On 8 August 2012 13:50, Mat Jaggard <matthew@jaggard.org.uk> wrote:
> Really? I think I must be missing something. When I plot them in excel
> I get the attached results...
>
>
> On 8 August 2012 13:23, Gilles Sadowski <gilles@harfang.homelinux.org> wrote:
>> 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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