MATLAB: VPA behavior, workaround requested

Question

Does anybody now a workaround for this behaviour of vpa?:

syms a b c
c=a+b;   a=1;   b=1;
vpa(c)
ans =
a + b

while

 vpa(a+b)

returns the expected ans=2. I know I could define c after a and b, but in my particular program (the above is just a minimal example), this is not possible. So I am looking for a simple workaround (vpa(char(c)) also does not work).

Answer 1

Use the subs function inside the vpa call:

syms a b c
c=a+b;   a=1;   b=1;
vpa(subs(c))

produces:

ans =
2.0