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| # Copyright (c) 2020 Johns Hopkins University (Shinji Watanabe) | |
| # 2020 Northwestern Polytechnical University (Pengcheng Guo) | |
| # 2020 Mobvoi Inc (Binbin Zhang) | |
| # 2024 Alibaba Inc (Xiang Lyu) | |
| # | |
| # 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. | |
| """Swish() activation function for Conformer.""" | |
| import torch | |
| from torch import nn, sin, pow | |
| from torch.nn import Parameter | |
| class Swish(torch.nn.Module): | |
| """Construct an Swish object.""" | |
| def forward(self, x: torch.Tensor) -> torch.Tensor: | |
| """Return Swish activation function.""" | |
| return x * torch.sigmoid(x) | |
| # Implementation adapted from https://github.com/EdwardDixon/snake under the MIT license. | |
| # LICENSE is in incl_licenses directory. | |
| class Snake(nn.Module): | |
| ''' | |
| Implementation of a sine-based periodic activation function | |
| Shape: | |
| - Input: (B, C, T) | |
| - Output: (B, C, T), same shape as the input | |
| Parameters: | |
| - alpha - trainable parameter | |
| References: | |
| - This activation function is from this paper by Liu Ziyin, Tilman Hartwig, Masahito Ueda: | |
| https://arxiv.org/abs/2006.08195 | |
| Examples: | |
| >>> a1 = snake(256) | |
| >>> x = torch.randn(256) | |
| >>> x = a1(x) | |
| ''' | |
| def __init__(self, in_features, alpha=1.0, alpha_trainable=True, alpha_logscale=False): | |
| ''' | |
| Initialization. | |
| INPUT: | |
| - in_features: shape of the input | |
| - alpha: trainable parameter | |
| alpha is initialized to 1 by default, higher values = higher-frequency. | |
| alpha will be trained along with the rest of your model. | |
| ''' | |
| super(Snake, self).__init__() | |
| self.in_features = in_features | |
| # initialize alpha | |
| self.alpha_logscale = alpha_logscale | |
| if self.alpha_logscale: # log scale alphas initialized to zeros | |
| self.alpha = Parameter(torch.zeros(in_features) * alpha) | |
| else: # linear scale alphas initialized to ones | |
| self.alpha = Parameter(torch.ones(in_features) * alpha) | |
| self.alpha.requires_grad = alpha_trainable | |
| self.no_div_by_zero = 0.000000001 | |
| def forward(self, x): | |
| ''' | |
| Forward pass of the function. | |
| Applies the function to the input elementwise. | |
| Snake ∶= x + 1/a * sin^2 (xa) | |
| ''' | |
| alpha = self.alpha.unsqueeze(0).unsqueeze(-1) # line up with x to [B, C, T] | |
| if self.alpha_logscale: | |
| alpha = torch.exp(alpha) | |
| x = x + (1.0 / (alpha + self.no_div_by_zero)) * pow(sin(x * alpha), 2) | |
| return x | |