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import torch
def get_sigmas(noise_scheduler, timesteps, n_dim=4, dtype=torch.float32, device=None):
sigmas = noise_scheduler.sigmas.to(device=device, dtype=dtype)
schedule_timesteps = noise_scheduler.timesteps.to(device)
timesteps = timesteps.to(device)
step_indices = [(schedule_timesteps == t).nonzero().item() for t in timesteps]
sigma = sigmas[step_indices].flatten()
while len(sigma.shape) < n_dim:
sigma = sigma.unsqueeze(-1)
return sigma
def SNR_to_betas(snr):
"""
Converts SNR to betas
"""
# alphas_cumprod = pass
# snr = (alpha / ) ** 2
# alpha_t^2 / (1 - alpha_t^2) = snr
alpha_t = (snr / (1 + snr)) ** 0.5
alphas_cumprod = alpha_t**2
alphas = alphas_cumprod / torch.cat(
[torch.ones(1, device=snr.device), alphas_cumprod[:-1]]
)
betas = 1 - alphas
return betas
def compute_snr(timesteps, noise_scheduler):
"""
Computes SNR as per Min-SNR-Diffusion-Training/guided_diffusion/gaussian_diffusion.py at 521b624bd70c67cee4bdf49225915f5
"""
alphas_cumprod = noise_scheduler.alphas_cumprod
sqrt_alphas_cumprod = alphas_cumprod**0.5
sqrt_one_minus_alphas_cumprod = (1.0 - alphas_cumprod) ** 0.5
# Expand the tensors.
# Adapted from Min-SNR-Diffusion-Training/guided_diffusion/gaussian_diffusion.py at 521b624bd70c67cee4bdf49225915f5
sqrt_alphas_cumprod = sqrt_alphas_cumprod.to(device=timesteps.device)[
timesteps
].float()
while len(sqrt_alphas_cumprod.shape) < len(timesteps.shape):
sqrt_alphas_cumprod = sqrt_alphas_cumprod[..., None]
alpha = sqrt_alphas_cumprod.expand(timesteps.shape)
sqrt_one_minus_alphas_cumprod = sqrt_one_minus_alphas_cumprod.to(
device=timesteps.device
)[timesteps].float()
while len(sqrt_one_minus_alphas_cumprod.shape) < len(timesteps.shape):
sqrt_one_minus_alphas_cumprod = sqrt_one_minus_alphas_cumprod[..., None]
sigma = sqrt_one_minus_alphas_cumprod.expand(timesteps.shape)
# Compute SNR.
snr = (alpha / sigma) ** 2
return snr
def compute_alpha(timesteps, noise_scheduler):
alphas_cumprod = noise_scheduler.alphas_cumprod
sqrt_alphas_cumprod = alphas_cumprod**0.5
sqrt_alphas_cumprod = sqrt_alphas_cumprod.to(device=timesteps.device)[
timesteps
].float()
while len(sqrt_alphas_cumprod.shape) < len(timesteps.shape):
sqrt_alphas_cumprod = sqrt_alphas_cumprod[..., None]
alpha = sqrt_alphas_cumprod.expand(timesteps.shape)
return alpha
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