Get the coefficients in a vector from cftool ?
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Hi,
In my script (*.m file), I would like to use cftool to get the 15 coefficients from a polynomial function (degrees 4) and put them in a vector. This vector will be use latter in my script. It have to be done without configuring the parameters in cftool windows. I would like everything to be automatic.
Any ideas to do it with cftool ? I already tried with fittype but it don't allow a so big z matrix (x and y are 1x17 vectors and z is a 17x17 matrix for example).
Kind regards, Seb
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Greig
2015년 2월 23일
편집: Greig
2015년 2월 23일
To extract the coefficients use the "fit" function....
[fitobject,gof,output]=fit([x, y], z, 'poly44');
fitobject.p00, fitobject.p10, fitobject.p01, etc contain all of the coefficients. So,
Coeffs = [fitobject.p00, fitobject.p10, fitobject.p01,....
is your vector of coefficients.
For more info type
doc fit
[Edit: First post was a solution for curve fitting, then I realised you were surface fitting.]
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Greig
2015년 2월 23일
You'll need to do some reshaping as fit expects column vectors for x, y and z. If I have my dimensions correct, something like this should work.
x2=reshape(meshgrid(x,y), numel(z), 1);
y2=repmat(y, 15, 1);
z2=reshape(z, numel(z), 1);
[fitobject,gof,output]=fit([x2, y2], z2, 'poly44');
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Seb Seb
2015년 2월 23일
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Greig
2015년 2월 23일
Sorry, I missed a transpose, it should be
y2=repmat(y', 15, 1);
y2 should now be 225x1.
The fit command expects x, y, and z to be column vectors. As it stands, you have x and y laid out like a coordinate system on which z can be laid. If you look at x2, the first 15 elements should all be the same, then the second 15 all the same and so on. The first 15 elements of y2 are y, then this repeats. In this way [x2,y2] represents all of the x-y coordinates in a long list. z is then reshaped to match this. cftool is smart enough to recognize this and does the reshaping internally.
I hope this makes sense.
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