![image.png|1000](https://imagehosting4picgo.oss-cn-beijing.aliyuncs.com/imagehosting/fix-dir%2Fpicgo%2Fpicgo-clipboard-images%2F2025%2F01%2F24%2F02-56-21-609d4f608183271e52fbb582766137b6-202501240256599-5424c3.png) $σ(x) =1/(1+\exp(-x))$