How get numeric values from symbolic function

Hi, I've defined a symbolic function st(t) and I'm trying to calculate the Fourier transform with the function of matlab fourier()

syms sf(f)
sf(f) = fourier(st(t),t,f);

but if I run the code

sf(1)

I get something like

ans = (1508120030528433*fourier(heaviside(fix(t) - t + 1/2)*heaviside(t - fix(t) - 2/5)*cos(2000000000*pi*t - 2328776796587809/2251799813685248), t, 1))/38685626227668133590597632 + (1508120030528433*fourier(heaviside(t - fix(t) - 3/5)*heaviside(fix(t) - t + 7/10)*cos(2000000000*pi*t - 2328776796587809/2251799813685248), t, 1))/38685626227668133590597632...

while if I run

ezplot(sf)

I get

Error in inline expression ==>
(6900523987068279.*fourier(cos(2000000000.*pi.*t
+
1282404220501851./562949953421312).*heaviside(t
- fix(t) - 1./5).*heaviside(fix(t)
- t + 3./10), t,
f))./154742504910672534362390528 +
(6900523987068279.*fourier(cos(2000000000.*pi.*t
+
1282404220501851./562949953421312).*heaviside(t
- fix(t) - 4./5).*heaviside(fix(t)
- t + 9./10), t,
f))./154742504910672534362390528 +
(6898037065725127.*fourier(heaviside(fix(t)
- t + 1./5).*heaviside(t - fix(t) -
1./10).*cos(2000000000.*pi.*t +
5130279707333783./2251799813685248),
t, f))./154742504910672534362390528
...
 Undefined function 'fourier' for
 input arguments of type 'double'.

Error in inline/feval (line 34)
        INLINE_OUT_ =
        inlineeval(INLINE_INPUTS_,
        INLINE_OBJ_.inputExpr,
        INLINE_OBJ_.expr);

Error in ezplotfeval (line 54)
    z = feval(f,x(1),y(1));

Error in ezplot>ezimplicit (line
258)
    u = ezplotfeval(f, X, Y);

Error in ezplot (line 154)
                hp =
                ezimplicit(cax,
                f{1}, vars, labels,
                args{:});

Error in sym/ezplot (line 61)
   h = ezplot(fhandle(f));

Error in calcolo_classico_s_di_w
(line 115)
ezplot(sf)

Also If I use

double(sf(1))

I get an error.

Could someone tell me how I can get numeric values of sf(f), like double(sf(1)), without errors? Thanks