🐛 fix cosine noise scheduler

Author: slavaheroes

monai/networks/schedulers/scheduler.py

@@ -105,10 +105,11 @@ def _cosine_beta(num_train_timesteps: int, s: float = 8e-3):
     x = torch.linspace(0, num_train_timesteps, num_train_timesteps + 1)
     alphas_cumprod = torch.cos(((x / num_train_timesteps) + s) / (1 + s) * torch.pi * 0.5) ** 2
     alphas_cumprod /= alphas_cumprod[0].item()
-    alphas = torch.clip(alphas_cumprod[1:] / alphas_cumprod[:-1], 0.0001, 0.9999)
-    betas = 1.0 - alphas
-    return betas, alphas, alphas_cumprod[:-1]
-
+    betas = 1.0 - (alphas_cumprod[1:] / alphas_cumprod[:-1])
+    betas = torch.clip(betas, 0.0, 0.999)
+    alphas = 1.0 - betas
+    alphas_cumprod = torch.cumprod(alphas, dim=0)
+    return betas, alphas, alphas_cumprod
 
 class Scheduler(nn.Module):
     """