How to convert solution of syms array to a normal array?

I am solving a series function, e.g. .

I want to get the obviously.

For my codes,

b = 2;
y = [1,2,3,4];
syms x [1 4]
S = solve(dot(repmat([a,b],4,1),[x;y].',2)==0);

The answer is

S = 
  struct with fields:

    x1: [1×1 sym]
    x2: [1×1 sym]
    x3: [1×1 sym]
    x4: [1×1 sym]

All I want is an array of [-2,-4,-6,-8]. How to get the array from this 'S' syms struct. Is there other better ways to solve this problem. The example function is a simple one. So it is impossible for me to use 'x = -1/a*b*y'.

Answer 1

[KSSV]

Read about double.

syms x y 
a = 1 ; b = 2 ; 
eqn = a*x+b*y==0 ; 
sol = solve(eqn,x) ; 
%
y = [1 2 3 4] ; 
iwant = double(subs(sol,y))

[wei zhang]

I think the 'subs' command is what I need more. Thank you.