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| import math | |
| import torch | |
| import torch.nn as nn | |
| def get_timestep_embedding( | |
| timesteps: torch.Tensor, | |
| embedding_dim: int, | |
| flip_sin_to_cos: bool = False, | |
| downscale_freq_shift: float = 1, | |
| scale: float = 1, | |
| max_period: int = 10000, | |
| ): | |
| """ | |
| This matches the implementation in Denoising Diffusion Probabilistic Models: Create sinusoidal timestep embeddings. | |
| :param timesteps: a 1-D Tensor of N indices, one per batch element. | |
| These may be fractional. | |
| :param embedding_dim: the dimension of the output. :param max_period: controls the minimum frequency of the | |
| embeddings. :return: an [N x dim] Tensor of positional embeddings. | |
| """ | |
| assert len(timesteps.shape) == 1, "Timesteps should be a 1d-array" | |
| half_dim = embedding_dim // 2 | |
| exponent = -math.log(max_period) * torch.arange( | |
| start=0, end=half_dim, dtype=torch.float32, device=timesteps.device | |
| ) | |
| exponent = exponent / (half_dim - downscale_freq_shift) | |
| emb = torch.exp(exponent) | |
| emb = timesteps[:, None].float() * emb[None, :] | |
| # scale embeddings | |
| emb = scale * emb | |
| # concat sine and cosine embeddings | |
| emb = torch.cat([torch.sin(emb), torch.cos(emb)], dim=-1) | |
| # flip sine and cosine embeddings | |
| if flip_sin_to_cos: | |
| emb = torch.cat([emb[:, half_dim:], emb[:, :half_dim]], dim=-1) | |
| # zero pad | |
| if embedding_dim % 2 == 1: | |
| emb = torch.nn.functional.pad(emb, (0, 1, 0, 0)) | |
| return emb | |
| class TimestepEmbedding(nn.Module): | |
| def __init__(self, channel: int, time_embed_dim: int, act_fn: str = "silu"): | |
| super().__init__() | |
| self.linear_1 = nn.Linear(channel, time_embed_dim) | |
| self.act = None | |
| if act_fn == "silu": | |
| self.act = nn.SiLU() | |
| self.linear_2 = nn.Linear(time_embed_dim, time_embed_dim) | |
| def forward(self, sample): | |
| sample = self.linear_1(sample) | |
| if self.act is not None: | |
| sample = self.act(sample) | |
| sample = self.linear_2(sample) | |
| return sample | |
| class Timesteps(nn.Module): | |
| def __init__(self, num_channels: int, flip_sin_to_cos: bool, downscale_freq_shift: float): | |
| super().__init__() | |
| self.num_channels = num_channels | |
| self.flip_sin_to_cos = flip_sin_to_cos | |
| self.downscale_freq_shift = downscale_freq_shift | |
| def forward(self, timesteps): | |
| t_emb = get_timestep_embedding( | |
| timesteps, | |
| self.num_channels, | |
| flip_sin_to_cos=self.flip_sin_to_cos, | |
| downscale_freq_shift=self.downscale_freq_shift, | |
| ) | |
| return t_emb | |