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89b84208aa
* add MMI to AIShell * fix MMI decode graph * export model * typo * fix code style * typo
99 lines
3.2 KiB
Python
99 lines
3.2 KiB
Python
# Copyright 2021 Xiaomi Corp. (authors: Fangjun Kuang)
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#
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# See ../../../../LICENSE for clarification regarding multiple authors
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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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import torch
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class LabelSmoothingLoss(torch.nn.Module):
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"""
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Implement the LabelSmoothingLoss proposed in the following paper
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https://arxiv.org/pdf/1512.00567.pdf
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(Rethinking the Inception Architecture for Computer Vision)
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"""
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def __init__(
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self,
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ignore_index: int = -1,
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label_smoothing: float = 0.1,
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reduction: str = "sum",
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) -> None:
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"""
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Args:
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ignore_index:
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ignored class id
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label_smoothing:
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smoothing rate (0.0 means the conventional cross entropy loss)
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reduction:
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It has the same meaning as the reduction in
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`torch.nn.CrossEntropyLoss`. It can be one of the following three
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values: (1) "none": No reduction will be applied. (2) "mean": the
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mean of the output is taken. (3) "sum": the output will be summed.
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"""
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super().__init__()
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assert 0.0 <= label_smoothing < 1.0
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self.ignore_index = ignore_index
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self.label_smoothing = label_smoothing
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self.reduction = reduction
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def forward(self, x: torch.Tensor, target: torch.Tensor) -> torch.Tensor:
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"""
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Compute loss between x and target.
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Args:
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x:
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prediction of dimension
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(batch_size, input_length, number_of_classes).
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target:
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target masked with self.ignore_index of
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dimension (batch_size, input_length).
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Returns:
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A scalar tensor containing the loss without normalization.
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"""
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assert x.ndim == 3
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assert target.ndim == 2
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assert x.shape[:2] == target.shape
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num_classes = x.size(-1)
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x = x.reshape(-1, num_classes)
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# Now x is of shape (N*T, C)
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# We don't want to change target in-place below,
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# so we make a copy of it here
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target = target.clone().reshape(-1)
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ignored = target == self.ignore_index
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target[ignored] = 0
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true_dist = torch.nn.functional.one_hot(
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target, num_classes=num_classes
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).to(x)
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true_dist = (
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true_dist * (1 - self.label_smoothing)
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+ self.label_smoothing / num_classes
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)
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# Set the value of ignored indexes to 0
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true_dist[ignored] = 0
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loss = -1 * (torch.log_softmax(x, dim=1) * true_dist)
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if self.reduction == "sum":
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return loss.sum()
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elif self.reduction == "mean":
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return loss.sum() / (~ignored).sum()
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else:
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return loss.sum(dim=-1)
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