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minor fix in diffusion edm schedule #560

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merged 1 commit into from
Aug 21, 2025
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minor fix in diffusion edm schedule #560

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6 changes: 3 additions & 3 deletions bayesflow/networks/diffusion_model/schedules/edm_noise_schedule.py
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,7 @@ def __init__(self, sigma_data: float = 1.0, sigma_min: float = 1e-4, sigma_max:
def get_log_snr(self, t: float | Tensor, training: bool) -> Tensor:
"""Get the log signal-to-noise ratio (lambda) for a given diffusion time."""
if training:
# SNR = -dist.icdf(t_trunc) # negative seems to be wrong in the Kingma paper
# SNR = dist.icdf(1-t) # Kingma paper wrote -F(t) but this seems to be wrong
loc = -2 * self.p_mean
scale = 2 * self.p_std
snr = loc + scale * ops.erfinv(2 * t - 1) * math.sqrt(2)
Expand All @@ -67,11 +67,11 @@ def get_log_snr(self, t: float | Tensor, training: bool) -> Tensor:
def get_t_from_log_snr(self, log_snr_t: float | Tensor, training: bool) -> Tensor:
"""Get the diffusion time (t) from the log signal-to-noise ratio (lambda)."""
if training:
# SNR = -dist.icdf(t_trunc) => t = dist.cdf(-snr) # negative seems to be wrong in the Kingma paper
# SNR = dist.icdf(1-t) => t = 1-dist.cdf(snr) # Kingma paper wrote -F(t) but this seems to be wrong
loc = -2 * self.p_mean
scale = 2 * self.p_std
x = log_snr_t
t = 0.5 * (1 + ops.erf((x - loc) / (scale * math.sqrt(2.0))))
t = 1 - 0.5 * (1 + ops.erf((x - loc) / (scale * math.sqrt(2.0))))
else: # sampling
# SNR = -2 * rho * log(sigma_max ** (1/rho) + (1 - t) * (sigma_min ** (1/rho) - sigma_max ** (1/rho)))
# => t = 1 - ((exp(-snr/(2*rho)) - sigma_max ** (1/rho)) / (sigma_min ** (1/rho) - sigma_max ** (1/rho)))
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