设矩阵元素的行下标为i，列下标为j，所有下标均从0开始计数，方阵阶数为n。
主对角线元素满足i == j，副对角线元素满足i + j == n - 1
i == j
i + j == n - 1
主对角线元素满足i == j，副对角线元素满足i + j == n
i + j == n
主对角线元素满足i + j == n - 1，副对角线元素满足i == j
主对角线元素满足i > j，副对角线元素满足i < j
i > j
i < j