Error using the FIT function

Hi All,

I have y data as function of x, or y = f(x).

I want to use the FIT function inside a script

My aim is to smooth y using the Smoothing Spline method and leave matlab to choose the smoothing parameter (similar to the "Default" option when doing the same action but using the Curve Fitting Toolbox)

The code I wrote so far is

y_fit = fit(x,y,'smoothingspline');

y_smooth = feval(y_fit,x);

However, I am getting the following error

Error in cfit/subsref (line 16)
          out = iParenthesesReference( obj, currsubs );

The error is given at the first line of my code shown above. Do you spot the mistake?

Thanks in advance

G