Error using cfit/subsref when trying to fit a smoothingspline

According to documentation, if a fittype is specified, the output becomes [curve,gof] = fit(x,y,fttype)

My code is shown as follows:

A = importdata('exp65_C1.SS');
[x,y] = prepareCurveData(A(:,1),A(:,2));
[fit_o,~] = fit(x,y,'smoothingspline');

I get the error:

Error using cfit/subsref
Too many output arguments.

When I execute the fit line. I checked that x and y are both single column vectors of size 12776x1, and both have the same dimensions. The data goes from 0 to 0.83 for x, and 0 to 726 for y.

When I remove the ~ since it said I have too many output arguments, it gives this error instead:

Error using cfit/subsref>iParenthesesReference (line 36)
Too many inputs to CFIT/SUBSREF.

Error in cfit/subsref (line 15)
        out = iParenthesesReference( obj, currsubs );

Which makes sense since fttype requires more than one output. Same error if I don't specify an output at all.

What is going on?

[Walter Roberson]

Which MATLAB release are you using?

R2015aSP1 is the oldest MATLAB version I have easy access to. The gof output is defined by R2015aSP1.

Answer 1

[Riya]

Hi Zhangxi,

I understand that you are encountering an error while trying to fit a "smoothingspline" to your dataset. I tried reproducing the issue with the following sample code:

clc; clear; close all;

% Generate synthetic data similar to yours  
x = linspace(0, 0.83, 12776)'; % Column vector 
y = linspace(0, 726, 12776)'.^1.5 + randn(12776,1)*10;

% Prepare curve data 
[xData, yData] = prepareCurveData(x, y);

% Attempt to fit with smoothingspline
[fit_o, gof] = fit(xData, yData, 'smoothingspline');

% Display outputs  
disp('Fitted Model:');
disp(fit_o);
disp('Goodness of Fit:'); 
disp(gof);

% Plot results
figure; 
plot(fit_o, xData, yData);
title('Smoothing Spline Fit'); 
xlabel('x');
ylabel('y');  
grid on;

This code is running successfully without any errors. It might be the case that there is some issue related to the dataset file “exp65_C1.SS” that you are using. You can try the following commands to make sure it contains numeric data and has the expected dimensions.

A = importdata('exp65_C1.SS'); 
size(A)   
whos A

You can also try running the provided sample code to verify that the functions are working fine. If the problem still exists, please share the “exp65_C1.SS” file that you are using so that I can further debug the issue.

For more information about fitting a smoothing spline curve, please refer the following documentation:

https://www.mathworks.com/help/curvefit/fit.html?lang=en#bto2vuv-7

Thanks!