Create arcmargin.py

ppcls/arch/head/arcmargin.py

+# Copyright (c) 2021 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle
+import paddle.nn as nn
+import math
+
+class ArcMargin(nn.Layer):
+    def __init__(self, embedding_size, 
+                       class_num,  
+                       margin=0.5, 
+                       scale=80.0, 
+                       easy_margin=False):
+        super(ArcMargin, self).__init__()
+        self.embedding_size   = embedding_size
+        self.class_num   = class_num
+        self.margin      = margin
+        self.scale       = scale
+        self.easy_margin = easy_margin
+
+        weight_attr =  paddle.ParamAttr(initializer = paddle.nn.initializer.XavierNormal())
+        self.fc = nn.Linear(self.embedding_size, self.class_dim, weight_attr=weight_attr, bias_attr=False) 
+
+    def forward(self, input, label):
+        input_norm = paddle.sqrt(paddle.sum(paddle.square(input), axis=1, keepdim=True))
+        input = paddle.divide(input, input_norm)
+
+        weight = self.fc0.weight
+        weight_norm = paddle.sqrt(paddle.sum(paddle.square(weight), axis=0, keepdim=True))
+        weight = paddle.divide(weight, weight_norm)
+        
+        cos   = paddle.matmul(input, weight)
+        sin   = paddle.sqrt(1.0 - paddle.square(cos) + 1e-6)
+        cos_m = math.cos(self.margin)
+        sin_m = math.sin(self.margin)
+        phi   = cos * cos_m - sin * sin_m
+
+        th = math.cos(self.margin) * (-1)
+        mm = math.sin(self.margin) * self.margin
+        if self.easy_margin:
+            phi = self._paddle_where_more_than(cos, 0, phi, cos)
+        else:
+            phi = self._paddle_where_more_than(cos, th, phi, cos - mm)
+
+        one_hot = paddle.nn.functional.one_hot(label, self.class_dim)
+        one_hot = paddle.squeeze(one_hot, axis=[1])
+        output  = paddle.multiply(one_hot, phi) + paddle.multiply((1.0 - one_hot), cos)
+        output  = output * self.scale
+        return output
+
+    def _paddle_where_more_than(self, target, limit, x, y):
+        mask   = paddle.cast( x = (target > limit), dtype='float32')
+        output = paddle.multiply(mask, x) + paddle.multiply((1.0 - mask), y)
+        return output