The sum of two matrices $$\mathbf{A}$$ and $$\mathbf{B}$$ (of the same dimensions) is a new matrix of the same dimensions, $$\mathbf{C}$$ = $$\mathbf{A}$$+ $$\mathbf{B}$$. The sum is defined by adding entries with the same indices: $$c_{ij}=a_{ij}+b_{ij}$$.
$\begin{pmatrix} 3 &-2 &4 \\ 5 &3i &3 \\ -i & 1/2 &9 \end{pmatrix}+\begin{pmatrix} 0 &2 &1 \\ -4 &-2i &i\\ -i & 1/2 &-5 \end{pmatrix}=\begin{pmatrix} 3 &0 &5 \\ 1 &i &3+i\\ -2i & 1 &4 \end{pmatrix} \nonumber$