# 矩阵计算
| $y$ | $a$ | $au$ | sum(x) |  |
| ---- | ---- | ---- | ---- | ---- |
| $\frac{\partial y}{\partial \mathbf x}$ | $0^T$ | $a \frac{\partial u}{\partial \mathbf x}$ | $1^T$ |  |