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fix numerical singularity at t=1.0. config files specify max_t=0.99. … #200

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fix numerical singularity at t=1.0. config files specify max_t=0.99. … #200

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3 changes: 2 additions & 1 deletion src/bioemu/sde_lib.py
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Expand Up @@ -162,7 +162,8 @@ def __init__(self, s: float = 0.008):

def beta(self, t) -> torch.Tensor:
# Derived from _marginal_mean_coeff using equation (29) in Song et al.
return torch.tan((t + self.s) / (1 + self.s) * np.pi / 2) * np.pi / (1 + self.s)
t_clamp = torch.clamp(t, max=1.0 - 1e-6) # clips t to avoid tan(π/2) singularity at t=1.0
return torch.tan((t_clamp + self.s) / (1 + self.s) * np.pi / 2) * np.pi / (1 + self.s)

def _marginal_mean_coeff(self, t: torch.Tensor) -> torch.Tensor:
mean_coeff = torch.cos((t + self.s) / (1 + self.s) * np.pi / 2) / self.c
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