how to get the coeffients out of a sfit object after creating it on some data using 'cubicinterp'.

Question

Simon Freutel 2017-7-18

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https://ww2.mathworks.cn/matlabcentral/answers/349238-how-to-get-the-coeffients-out-of-a-sfit-object-after-creating-it-on-some-data-using-cubicinterp

评论： Antonio Machado Jorge 2023-10-17

Hi, i want to fit some 3d data, and generate a mathematical description of the surface using the curve fitting toolbox. I used "cubicinterp" as the interpolation method and get the following output:

>> test = fit([X_cart,Y_cart],Z_cart,'cubicinterp','Exclude', nanz) Warning: Duplicate x-y data points detected: using average of the z values. > In curvefit.attention.Warning/throw (line 30) In curvefit.model.SurfaceInterpolantFactory/doCoalesceDuplicatePoints (line 206) In curvefit.model.SurfaceInterpolantFactory/create (line 74) In fit>iSurfaceInterpolation (line 895) In fit>iFit (line 489) In fit (line 108)

     Piecewise cubic interpolant:
       test(x,y) = piecewise cubic surface computed from p
     Coefficients:
       p = coefficient structure

I have no idea how to extract the coefficients or any kind of mathematical description out of the sfit object "test" which is generated.

Any ideas?

Thanks for any help.

Simon

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Answer 1

Mukul Rao 2017-7-21

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https://ww2.mathworks.cn/matlabcentral/answers/349238-how-to-get-the-coeffients-out-of-a-sfit-object-after-creating-it-on-some-data-using-cubicinterp#answer_275040

Hi,

Here is an example that demonstrates how to extract fit coefficients from the "sfit" object:

coeffvalues

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Simon Freutel 2017-7-24

Hi,

thanks, but I guess this only works for cfit objects. Not for sfit?!

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Answer 2

haochen he 2018-11-30

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https://ww2.mathworks.cn/matlabcentral/answers/349238-how-to-get-the-coeffients-out-of-a-sfit-object-after-creating-it-on-some-data-using-cubicinterp#answer_349726

在 MATLAB Online 中打开

I think we do not have access to the model parameters:

[fitresult, gof] = fit( [xData, yData], zData, 'cubicinterp', 'Normalize', 'on' );
names = coeffnames(fitresult); % result is: names = {'p'}
% if you try other properties like 'fitresult.others', an error will goes like:
% For the current fit, you can access these properties: p
% then we try this:
names = coeffnames(fitresult.p);
% result will be an error, if we see the fitresult.p, we can only find the property is Type='Cubic'

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Antonio Leanza 2022-1-20

编辑：Antonio Leanza 2022-1-20

names = fitresult.p.coefs works

Antonio Machado Jorge 2023-10-17

在 MATLAB Online 中打开

It doesn't work for me... I'm on 2023b

>> fitresult.p
ans = 
  GriddataInterpolant with properties:
    Type: 'Cubic'
   
    
>> names = fitresult.p.coefs
Unrecognized method, property, or field
'coefs' for class
'curvefit.model.GriddataInterpolant'.
Error in indexing (line 26)
    out = subsref(out, subs);