problem with CSAPS (cubic smoothing spline)

Hi!

I am having trouble using CSAPS function. Consider a slightly modified example from matlab manual

 x = linspace(0,2*pi,21); y = sin(x)+(rand(1,21)-.5)*.1;
 pp = csaps(x,y, .4)

Changing the smoothing parameter p, which is equal 0.4 in the case above, gives you different fitting curves. However, if I extend the range of data sites, say x=linspace(0,100*pi,21), then no matter which value of smoothing parameter p I use it gives me exactly the same curve. Conversely, if I shrink the interval then it gives me just a straight line irregardless of the p-value. Any thoughts?

Thanks!

Answer 1

[Isabella Osetinsky-Tzidaki]

Your n=21 in linspace is too small for influencing your 0-100*pi range curve