I want to consider this simple problem:
$$\min f(x) := x^TQx + qx + r$$ $$s.t.{\ {\ }} -1 \leq x_i \leq 1 {\ {\ }} for {\ {\ }} i = 1,2,3 $$
where
$$ Q = \begin{pmatrix} 13 & 12 & -2 \\ 12 & 17 & 6 \\ -2 & 6 & 12 \end{pmatrix} , \qquad q = \begin{pmatrix} -22 \\ -13.5 \\ 13 \end{pmatrix}, \qquad r = 1 $$
From here, I can't tell what is the dimension of $x$.