minimum of csaps smoothing spline

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Shaun Werkhoven
Shaun Werkhoven 2013-4-28
the spline smoothing function csaps finds the minimum of a fitting term and a smoothness term .. but can u get this minimum value? I want to try different values of p (which controls the tradeoff between smoothness and fit) and look at the minimum value, but I cant see how to actually get the value.
Thx, Shaun
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Shaun Werkhoven
Shaun Werkhoven 2013-4-30
I should have said I want the minimum value of the spline fit, ie.
min[ p(y-f(x))^2 + (1-p)Int((D^2)(f))^2 ]
= min value

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回答（1 个）

Matt J
Matt J 2013-4-28
编辑：Matt J 2013-4-28
pp = csaps(x,y,p);
[~,idx]=min(ppval(pp,x)); %initial guess of min location
[xmin,ymin]=fminsearch(@(z)ppval(pp,z), x(idx)); %refine the min
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Shaun Werkhoven
Shaun Werkhoven 2013-4-30
thanks for ur answer but this is not what I meant .. I guess I didnt make it clear enough. I dont want the minimum y value, I want the minimum value of the spline fit, ie.
min[ p(y-f(x))^2 + (1-p)Int((D^2)(f))^2 ]
= min value
csaps calculates this minimum over ppform functions f, but can u get this value of the minimum returned?
Matt J
Matt J 2013-4-30
编辑：Matt J 2013-4-30
It does not appear from "doc csaps" that CSAPS will give it to you directly, but you could evaluate the function yourself using the information available from UNMKPP.
If CSAPS is an mfile, you might also be able to dig the necessary code out of there directly, or make a modified version of the code that will return the fitting error.

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