Tests if a matrix is antidiagonal.
Ais a matrix
εis a positive number
A is a matrix then
IsAntidiagonal(A, ε) is
A is square and i ≠ n − j + 1 implies A[i, j] is zero (with epsilon
n is the size of
IsAntidiagonal(❨❨0, 4❩, ❨1, 0❩❩)