交叉熵Loss 2026-09-07 Lishengxie网课学习:https://haoailab.com/cse234-w25/ Week2 autodiff 章节问题推导L=-\sum t_{i}\log(y_{i}),y_{i}=\text{softmax}\left(x\right)_{i}=\frac{e^{x_{i}}}{\sum e^{x_{d}}}