dpb
Posts:
8,362
Registered:
6/7/07


Re: Numerical integration of polyfit coefficients
Posted:
Dec 12, 2013 1:57 PM


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.


