This is LaTeX code:
[latex]
S_1 = \begin{bmatrix} 1 & 0 \\ 0 & 0 \end{bmatrix}, \quad S_2 = \begin{bmatrix} 1 & 2 \\ 0 & 0 \end{bmatrix}, \quad S_3 = \begin{bmatrix} 1 & 2 \\ 3 & 0 \end{bmatrix}
[/latex]