Curve Fitting in MATLAB: Error Diagnosis

[ergospherical]

I have two 1D matrices X(1,j) and Y(1,j) of equal length. To fit Y to a model asin(bx) I tried:

fit = fittype(@(a,b,X), a*sin(b*X));
[fitted, gof] = fit(X, Y, fit)
coefficients = coeffvalues(fitted)

this gives the message: Error using fittype>iDeduceCoefficients
The independent variable x does not appear in the equation expression.
Use x in the expression or indicate another variable as the independent variable.

What's wrong?

 

[Wrichik Basu]

By default, fittype uses small x as the variable name. If you use something else, you have to specify that:

fit = fittype(@(a,b,X), a*sin(b*X), 'independent', {'X'});

See this portion in the documentation: https://in.mathworks.com/help/curvefit/fittype.html?s_tid=doc_ta#btpxtcd-6

And this example: https://in.mathworks.com/help/curvefit/fittype.html?s_tid=doc_ta#btpaend-11

 

[ergospherical]

sweet, thanks