MATLAB: Can I make a spline both smoothing *and* periodic

csapeperiodicsmoothingspapsspline

Hi all,
I would like to make a smoothing spline through data, and enforce point and gradient equality at either end of my spline. Here's the data:
XYpts = [...
    10     5    -5   -10    -5    0    10
     0     9     9     0    -9    0     0];
figure, plot(XYpts(1,:), XYpts(2,:),'bo')
axis equal, grid on, hold on
And here I can do a smoothing spline without the constraints to make it periodic (note that it smooths the original data nicely, but meets a nasty sharp turn at the end):
dt = sum((diff(XYpts,[],2).^2));
t = cumsum([0,dt.^(0.25)]);
smoothingSpline = spaps(t,XYpts,1);
fnplt(smoothingSpline,'-r.')
And here I can do an interpolating spline with the correct continuity constraints I'm looking for:
interpolatingSpline = csape(t,XYpts,'periodic') 
fnplt(interpolatingSpline,'-g.')
But neither of these do both at the same time (smooth the data and enforce continuity). Can you help?
The only way I can think of so far is a bit messy: repeat the starting/ending points of my data so that the smoothed spline wraps back over itself, and then only sample it within the "original" domain. Is there a better/cleaner way?
Thanks, Sven.

Best Answer

This FEX file advertises all kinds of convenient options for constraining spline fits,
http://www.mathworks.com/matlabcentral/fileexchange/24443-slm-shape-language-modeling
You need the Optimization Toolbox, though.
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