Polynomial fitting prob lem

Hello,

Would anyone have an idea how to prevent these large peaks and troughs occurring at the edges of a polynomial fit?

    x = -1:0.005:1;               

    y = rand(size(x));   

    polydegree = 15;    

    coeffs = polyfit(x, y, polydegree);

    y = polyval(coeffs,x); 
plot(x,y,'k')

[Tom]

ooh, for instance - is there a way to constrain the polyfit so that the start and end points are always 0?

Answer 1

[Jan]

Searching for already published solutions in the net is a good idea, see:

• http://www.mathworks.com/matlabcentral/fileexchange/38926-fit-polynomial-to-data-with-constraints
• http://www.mathworks.com/matlabcentral/fileexchange/35401-polyfitzero
• http://www.mathworks.com/matlabcentral/fileexchange/220-polyfit2
• http://www.mathworks.com/matlabcentral/fileexchange/272-polyfit0-m/content/polyfit0.m

But interpolating polynomials must oscillate at the edges for high orders. Therefore the order should be chosen as low as possible.