File size: 3,097 Bytes
eb71a72 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 | import math
import numpy as np
import torch
from einops import rearrange, reduce, repeat
from einops.layers.torch import Rearrange
from torch import nn
# absolute positional embedding used for vanilla transformer sequential data
class PositionalEncoding(nn.Module):
def __init__(self, d_model, dropout=0.1, max_len=500, batch_first=False):
super().__init__()
self.batch_first = batch_first
self.dropout = nn.Dropout(p=dropout)
pe = torch.zeros(max_len, d_model)
position = torch.arange(0, max_len).unsqueeze(1)
div_term = torch.exp(torch.arange(0, d_model, 2) * (-np.log(10000.0) / d_model))
pe[:, 0::2] = torch.sin(position * div_term)
pe[:, 1::2] = torch.cos(position * div_term)
pe = pe.unsqueeze(0).transpose(0, 1)
self.register_buffer("pe", pe)
def forward(self, x):
if self.batch_first:
x = x + self.pe.permute(1, 0, 2)[:, : x.shape[1], :]
else:
x = x + self.pe[: x.shape[0], :]
return self.dropout(x)
# very similar positional embedding used for diffusion timesteps
class SinusoidalPosEmb(nn.Module):
def __init__(self, dim):
super().__init__()
self.dim = dim
def forward(self, x):
device = x.device
half_dim = self.dim // 2
emb = math.log(10000) / (half_dim - 1)
emb = torch.exp(torch.arange(half_dim, device=device) * -emb)
emb = x[:, None] * emb[None, :]
emb = torch.cat((emb.sin(), emb.cos()), dim=-1)
return emb
# dropout mask
def prob_mask_like(shape, prob, device):
if prob == 1:
return torch.ones(shape, device=device, dtype=torch.bool)
elif prob == 0:
return torch.zeros(shape, device=device, dtype=torch.bool)
else:
return torch.zeros(shape, device=device).float().uniform_(0, 1) < prob
def extract(a, t, x_shape):
b, *_ = t.shape
out = a.gather(-1, t)
return out.reshape(b, *((1,) * (len(x_shape) - 1)))
def make_beta_schedule(
schedule, n_timestep, linear_start=1e-4, linear_end=2e-2, cosine_s=8e-3
):
if schedule == "linear":
betas = (
torch.linspace(
linear_start ** 0.5, linear_end ** 0.5, n_timestep, dtype=torch.float64
)
** 2
)
elif schedule == "cosine":
timesteps = (
torch.arange(n_timestep + 1, dtype=torch.float64) / n_timestep + cosine_s
)
alphas = timesteps / (1 + cosine_s) * np.pi / 2
alphas = torch.cos(alphas).pow(2)
alphas = alphas / alphas[0]
betas = 1 - alphas[1:] / alphas[:-1]
betas = np.clip(betas, a_min=0, a_max=0.999)
elif schedule == "sqrt_linear":
betas = torch.linspace(
linear_start, linear_end, n_timestep, dtype=torch.float64
)
elif schedule == "sqrt":
betas = (
torch.linspace(linear_start, linear_end, n_timestep, dtype=torch.float64)
** 0.5
)
else:
raise ValueError(f"schedule '{schedule}' unknown.")
return betas.numpy()
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