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| # Implementation adapted from https://github.com/EdwardDixon/snake under the MIT license. | |
| # LICENSE is in incl_licenses directory. | |
| import torch | |
| from torch import nn, sin, pow | |
| from torch.nn import Parameter | |
| 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 | |
| class SnakeBeta(nn.Module): | |
| """ | |
| A modified Snake function which uses separate parameters for the magnitude of the periodic components | |
| Shape: | |
| - Input: (B, C, T) | |
| - Output: (B, C, T), same shape as the input | |
| Parameters: | |
| - alpha - trainable parameter that controls frequency | |
| - beta - trainable parameter that controls magnitude | |
| References: | |
| - This activation function is a modified version based on this paper by Liu Ziyin, Tilman Hartwig, Masahito Ueda: | |
| https://arxiv.org/abs/2006.08195 | |
| Examples: | |
| >>> a1 = snakebeta(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 that controls frequency | |
| - beta - trainable parameter that controls magnitude | |
| alpha is initialized to 1 by default, higher values = higher-frequency. | |
| beta is initialized to 1 by default, higher values = higher-magnitude. | |
| alpha will be trained along with the rest of your model. | |
| """ | |
| super(SnakeBeta, 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) | |
| self.beta = Parameter(torch.zeros(in_features) * alpha) | |
| else: # Linear scale alphas initialized to ones | |
| self.alpha = Parameter(torch.ones(in_features) * alpha) | |
| self.beta = Parameter(torch.ones(in_features) * alpha) | |
| self.alpha.requires_grad = alpha_trainable | |
| self.beta.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. | |
| SnakeBeta ∶= x + 1/b * sin^2 (xa) | |
| """ | |
| alpha = self.alpha.unsqueeze(0).unsqueeze(-1) # Line up with x to [B, C, T] | |
| beta = self.beta.unsqueeze(0).unsqueeze(-1) | |
| if self.alpha_logscale: | |
| alpha = torch.exp(alpha) | |
| beta = torch.exp(beta) | |
| x = x + (1.0 / (beta + self.no_div_by_zero)) * pow(sin(x * alpha), 2) | |
| return x | |