loss函数之margin改进方法

最近sphereface人脸方法是目前开源人脸中最有效的方法，通过改进我也获得了lfw acc 99.7%的结果，下面几篇也是对sphereface改进的论文：

AM : Additive Margin Softmax for Face Verification

AAM : Face Recognition via Centralized Coordinate Learning

ArcFace: ArcFace: Additive Angular Margin Loss for Deep Face Recognition