3jiao

代码说明：

  上三角或下三角矩阵也有大部份的元素不储存值（为0），我们可以将它们使用一维阵列来储存以节省储存空间，而对称矩阵因为对称于对角线，所以可以视为上三角或下三角矩阵来储存。(Upper or lower triangular matrix or a large majority of elements are not stored value (0), we can use them to store a one-dimensional array in order to save storage space, and because the symmetrical diagonal symmetric matrix, it can be regarded as the or lower triangular matrix storage.)