Tensorflow实现何凯明的Focal Loss, 该损失函数主要用于解决分类问题中的类别不平衡
focal_loss_sigmoid: 二分类loss
focal_loss_softmax: 多分类loss
Reference Paper : Focal Loss for Dense Object Detection
Dr-Zhuang/focal-loss
Tensorflow version implementation of focal loss for binary and multi classification
Python