circlemargin.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 math
import paddle
import paddle.nn as nn
import paddle.nn.functional as F
 
class CircleMargin(nn.Layer):
    def __init__(self, embedding_size, 
                       class_num, 
                       margin, 
                       scale):
        super(CircleSoftmax, self).__init__()
        self.scale  = scale
        self.margin = margin
        self.embedding_size = embedding_size
        self.class_num = class_num

        weight_attr = paddle.ParamAttr(initializer = paddle.nn.initializer.XavierNormal())
        self.fc0 = paddle.nn.Linear(self.embedding_size, self.class_num, weight_attr=weight_attr)
 
    def forward(self, input, label):
        feat_norm = paddle.sqrt(paddle.sum(paddle.square(input), axis=1, keepdim=True))
        input = paddle.divide(input, feat_norm)

        weight = self.fc0.weight
        weight_norm = paddle.sqrt(paddle.sum(paddle.square(weight), axis=0, keepdim=True))
        weight = paddle.divide(weight, weight_norm)
 
        logits   = paddle.matmul(input, weight)

        alpha_p = paddle.clip(-logits.detach() + 1 + self.margin, min=0.)
        alpha_n = paddle.clip(logits.detach() + self.margin, min=0.)
        delta_p = 1 - self.margin
        delta_n = self.margin
        index = paddle.fluid.layers.where(label != -1).reshape([-1])
        m_hot = F.one_hot(label.reshape([-1]), num_classes=logits.shape[1])
        logits_p = alpha_p * (logits - delta_p)
        logits_n = alpha_n * (logits - delta_n)
        pre_logits = logits_p * m_hot + logits_n * (1 - m_hot)
        pre_logits = self.scale * pre_logits
 
        return pre_logits