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Topic: Numerical integration of polyfit coefficients
Replies: 6   Last Post: Dec 12, 2013 5:50 PM

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dpb

Posts: 8,298
Registered: 6/7/07
Re: Numerical integration of polyfit coefficients
Posted: Dec 12, 2013 1:57 PM
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On 12/12/2013 11:56 AM, Rajin wrote:
> Hello,
>
> I have the coefficients of a polynomial of order 12 given to me using
> polyfit (it was fitted to model a probability density function). I now
> need to use the given polynomial f(x), multiply it by x^2, and integrate
> it over a given boundary.
>
> I have tried using the integral function: integral(fun,xmin,xmax), where:
> fun = @(x) poly2sym(f) and f is the coefficients given by polyfit, but
> this doesn't work.
>
> Any ideas? Apologies if this seems trivial, I have tried everything!


Well, as another said, using a 12th order polynomial is asking for
trouble although that isn't _necessarily_ the problem.

The one obvious is that a polynomial integral can be computed
analytically from the coefficients by the power rule of integration and
then evaluated as needed.

Whether the result will be other than nonsensical is indeterminate w/o
some way to evaluate the data and the fit thereof.

Again, try something of much lower order polynomial like a cubic spline
or somesuch, or a better functional form.

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