It's not common to close that brace when writing math. (I've not seen it.)
Another thing I find confusing are the braces around ℤ × ℤ. They seem to be unnecessary (it wouldn’t make much sense for ∈ to have higher precedence than ×), and/or would imply a singleton set containing the set ℤ × ℤ as its only element.
A_ij = { 1 if (i,j) ∈ E
{ 0 otherwise
where
A ∈ ℝ^(n × n)
E ∈ { ℤ × ℤ }
n ∈ ℤ A_ij = ⎰ 1 if (i,j) ∈ E
⎱ 0 otherwise
where
A ∈ ℝ^(n × n)
E ∈ { ℤ × ℤ }
n ∈ ℤWe do support the Unicode ⎡|⎦ symbols for matrices. The grammar is that a matrix starts with either [ or ⎡ and ends with either ] or ⎦. Rows can be optionally surrounded by |. I find this too cumbersome to use myself.
A_ij = | 1 if (i,j) ∈ E
| 0 otherwise
where
A ∈ ℝ^(n × n)
E ∈ { ℤ × ℤ }
n ∈ ℤ