MATLAB: Does Matlab substitute a number in a formula instead of solving it

MATLABsymbolic

Using the Symbolic toolbox, Matlab seems to arbitrarily determine whether or not to return a solved value when a concrete value is substituted in a formula.
>> syms x
>> f(x) = 1/(5+4*cos(x))
>> f(0)
ans = 1/9
>> f(1)
ans = 1/(4*cos(1) + 5)
Why isn't it solving for f(1) ? I'm guessing its because I'm working symbolically, so I can substitute a second equation as x, but how I can force Matlab to return a concrete value?
EDIT: I tried double(f(1)) and that seemed to work. Would that be considered best practice here?

Best Answer

The Symbolic Math Toolbox outputs its results as symbolic expressions, unless you ask it to do otherwise. (It assumes you want a symbolic result.) The double function is not always appropriate for symbolic results, since if the symbolic result contains a symbolic variable, double will throw an error.
If you want a numeric result, use the vpa() function: 
syms x
f(x) = 1/(5+4*cos(x))
Out1 = f(0)
Out2 = f(1)
Out3 = vpa(f(1))
producing: 
Out1 =
1/9
 
Out2 =
1/(4*cos(1) + 5)
 
Out3 = 
0.1396412210276252254724967860432
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