矩阵的上下带宽是通过找到包含非零值的最后一条对角线(分别位于主对角线上方或下方)来测量的。
That is, for a matrixA带元素Aij公司:
Note that this measurement does not disallow intermediate diagonals in a band from being all zero, but instead focuses on the location of the last diagonal containing nonzeros. By convention, the upper and lower bandwidths of an empty matrix are both zero.