How to export a fourier series in its function form after using the curve-fitting method?

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I have constructed the following fitting for some periodic data y(:,1), so

theta_fit = fit(t,y(:,1),'fourier8'),

theta_fit =

     General model Fourier8:
     theta_fit(x) = 
               a0 + a1*cos(x*w) + b1*sin(x*w) + 
               a2*cos(2*x*w) + b2*sin(2*x*w) + a3*cos(3*x*w) + b3*sin(3*x*w) + 
               a4*cos(4*x*w) + b4*sin(4*x*w) + a5*cos(5*x*w) + b5*sin(5*x*w) + 
               a6*cos(6*x*w) + b6*sin(6*x*w) + a7*cos(7*x*w) + b7*sin(7*x*w) + 
               a8*cos(8*x*w) + b8*sin(8*x*w)

I know I can plot them using

plot(t,theta_fit(t),'r')

But then how do I extract theta_fit(x) as a symbolic functio, such that I can use theta_fit(t) in some other programs?