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How can I fit data using quartic smoothing splines?

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Dear Community,
I am looking for something exactly like the existing function SPAPS, but for quartic splines. For some reason the only built-in options appear to be quadratic, cubic, and quintic. I have tried solutions with the FIT function but I am not getting anywhere. Please note it is important that I can set knots, specify the smoothing parameter p and retract the values of the resulting function.
Thank you very much for your help!
Thomas
  3 Comments
Thomas Erdosi
Thomas Erdosi on 28 Jul 2012
I need to exactly replicate the results of a paper that uses quartic

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Answers (2)

Isabella Osetinsky-Tzidaki
Edited: Isabella Osetinsky-Tzidaki on 26 Dec 2016
Quoted from https://www.mathworks.com/help/curvefit/examples/how-to-construct-splines.html
k = 5; % order 5, i.e., we are working with quartic splines
x = 2*pi*sort([0 1 rand(1,10)]);
y = cos(x);
sp = spapi( optknt(x,k), x, y );

Azzi Abdelmalek
Azzi Abdelmalek on 28 Jul 2012
%let us take this example:
method='smoothingspline'
t=[0:10];y=sin(t); %your signal
yfit=fit(t',y',method) %interpolation function yfit
%now choose your new time vector with 0.1 sample time
ti=0:0.1:10;yi=yfit(ti)
plot(t,y,'r') %your original signal
hold on, plot(ti,yi,'+b'); %your new signal
  2 Comments
Thomas Erdosi
Thomas Erdosi on 28 Jul 2012
Thank you for your answer. I have tried the same before using the fit function with specifying 'smoothingspline' as method but unfortunately this is more of a general smoothing solution and not the exact quartic smoothing spline I need. I have tried a few thing with fitoptions as well but without success. Does anybody know how to do this for the quartic smoothing spline? Thanks again
Thomas Erdosi
Thomas Erdosi on 30 Jul 2012
Isn't there anyone who can help..? This must be possible to do in MATLAB.

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