116 lines
4.7 KiB
Python
116 lines
4.7 KiB
Python
# Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from __future__ import absolute_import
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from __future__ import division
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from __future__ import print_function
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import paddle
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import paddle.nn as nn
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class TripletAngularMarginLoss(nn.Layer):
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"""A more robust triplet loss with hard positive/negative mining on angular margin instead of relative distance between d(a,p) and d(a,n).
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Args:
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margin (float, optional): angular margin. Defaults to 0.5.
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normalize_feature (bool, optional): whether to apply L2-norm in feature before computing distance(cos-similarity). Defaults to True.
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reduction (str, optional): reducing option within an batch . Defaults to "mean".
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add_absolute (bool, optional): whether add absolute loss within d(a,p) or d(a,n). Defaults to False.
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absolute_loss_weight (float, optional): weight for absolute loss. Defaults to 1.0.
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ap_value (float, optional): weight for d(a, p). Defaults to 0.9.
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an_value (float, optional): weight for d(a, n). Defaults to 0.5.
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feature_from (str, optional): which key feature from. Defaults to "features".
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"""
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def __init__(self,
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margin=0.5,
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normalize_feature=True,
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reduction="mean",
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add_absolute=False,
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absolute_loss_weight=1.0,
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ap_value=0.9,
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an_value=0.5,
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feature_from="features"):
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super(TripletAngularMarginLoss, self).__init__()
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self.margin = margin
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self.feature_from = feature_from
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self.ranking_loss = paddle.nn.loss.MarginRankingLoss(
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margin=margin, reduction=reduction)
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self.normalize_feature = normalize_feature
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self.add_absolute = add_absolute
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self.ap_value = ap_value
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self.an_value = an_value
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self.absolute_loss_weight = absolute_loss_weight
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def forward(self, input, target):
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"""
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Args:
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inputs: feature matrix with shape (batch_size, feat_dim)
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target: ground truth labels with shape (num_classes)
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"""
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inputs = input[self.feature_from]
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if self.normalize_feature:
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inputs = paddle.divide(
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inputs, paddle.norm(
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inputs, p=2, axis=-1, keepdim=True))
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bs = inputs.shape[0]
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# compute distance(cos-similarity)
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dist = paddle.matmul(inputs, inputs.t())
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# hard negative mining
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is_pos = paddle.expand(target, (
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bs, bs)).equal(paddle.expand(target, (bs, bs)).t())
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is_neg = paddle.expand(target, (
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bs, bs)).not_equal(paddle.expand(target, (bs, bs)).t())
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# `dist_ap` means distance(anchor, positive)
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# both `dist_ap` and `relative_p_inds` with shape [N, 1]
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dist_ap = paddle.min(paddle.reshape(
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paddle.masked_select(dist, is_pos), (bs, -1)),
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axis=1,
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keepdim=True)
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# `dist_an` means distance(anchor, negative)
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# both `dist_an` and `relative_n_inds` with shape [N, 1]
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dist_an = paddle.max(paddle.reshape(
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paddle.masked_select(dist, is_neg), (bs, -1)),
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axis=1,
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keepdim=True)
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# shape [N]
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dist_ap = paddle.squeeze(dist_ap, axis=1)
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dist_an = paddle.squeeze(dist_an, axis=1)
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# Compute ranking hinge loss
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y = paddle.ones_like(dist_an)
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loss = self.ranking_loss(dist_ap, dist_an, y)
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if self.add_absolute:
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absolut_loss_ap = self.ap_value - dist_ap
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absolut_loss_ap = paddle.where(absolut_loss_ap > 0,
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absolut_loss_ap,
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paddle.zeros_like(absolut_loss_ap))
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absolut_loss_an = dist_an - self.an_value
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absolut_loss_an = paddle.where(absolut_loss_an > 0,
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absolut_loss_an,
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paddle.ones_like(absolut_loss_an))
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loss = (absolut_loss_an.mean() + absolut_loss_ap.mean()
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) * self.absolute_loss_weight + loss.mean()
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return {"TripletAngularMarginLoss": loss}
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