feat: training and sampling

src/simple_ddpm/model.py

@@ -23,18 +23,54 @@ class Conv(nn.Module):
     def __init__(self, in_channels: int, out_channels: int):
         super(Conv, self).__init__()
 
-        self.conv = nn.Sequential(
-            nn.Conv2d(in_channels, out_channels, kernel_size=3, padding=1),
-            nn.BatchNorm2d(num_features=out_channels),
-            nn.SiLU(),
-            nn.Conv2d(out_channels, out_channels, kernel_size=3, padding=1),
-            nn.BatchNorm2d(num_features=out_channels),
-            # nn.SiLU(),
-            nn.Dropout(0.1),
+        self.in_channels = in_channels
+
+        self.t_emb_layer = nn.Sequential(
+            nn.SiLU(), nn.Linear(T_EMBEDDING_SIZE, in_channels)
         )
 
-    def forward(self, x: torch.Tensor) -> torch.Tensor:
-        return self.conv(x)
+        self.conv = nn.ModuleList(
+            [
+                nn.Sequential(
+                    nn.GroupNorm(8, in_channels),
+                    nn.SiLU(),
+                    nn.Conv2d(in_channels, in_channels, kernel_size=3, padding=1),
+                ),
+                nn.Sequential(
+                    nn.GroupNorm(8, in_channels),
+                    nn.SiLU(),
+                    nn.Conv2d(in_channels, in_channels, kernel_size=3, padding=1),
+                ),
+            ]
+        )
+
+        self.sa_norm = nn.GroupNorm(8, in_channels)
+        self.sa = nn.MultiheadAttention(in_channels, 4, dropout=0.1, batch_first=True)
+
+        self.out_conv = nn.Conv2d(in_channels, out_channels, kernel_size=3, padding=1)
+
+    def forward(self, x: torch.Tensor, t_emb: torch.Tensor) -> torch.Tensor:
+        """Forward pass.
+        Input:
+            x (torch.Tensor): input of shape (B, C, H, W)
+            t_emb (torch.Tensor): embedding time input (B, t_emb)
+        """
+        B, _, H, W = x.shape
+        x_res = self.conv[0](x)
+        x_res = x_res + self.t_emb_layer(t_emb).view(B, self.in_channels, 1, 1).expand(
+            B, self.in_channels, H, W
+        )
+        x = x + self.conv[1](x_res)
+
+        C = x.shape[1]
+        in_att = self.sa_norm(x.reshape(B, C, -1)).transpose(1, 2)
+        out_att, _ = self.sa(in_att, in_att, in_att)
+        out_att = out_att.transpose(1, 2).reshape(B, C, H, W)
+        x = x + out_att
+
+        x = self.out_conv(x)
+
+        return x
 
 
 class Downsample(nn.Module):
@@ -76,9 +112,11 @@ class UNet(nn.Module):
             sinusoidal_positional_embedding(nb_timesteps, T_EMBEDDING_SIZE),
         )
 
+        self.preconv = nn.Conv2d(in_channels, 64, kernel_size=3, padding=1)
+
         self.encoder = nn.ModuleList(
             [
-                Conv(in_channels + T_EMBEDDING_SIZE, 64),
+                Conv(64, 64),
                 Conv(64, 128),
                 Conv(128, 256),
                 Conv(256, 512),
@@ -94,32 +132,33 @@ class UNet(nn.Module):
                 Conv(2 * 512, 256),
                 Conv(2 * 256, 128),
                 Conv(2 * 128, 64),
-                Conv(2 * 64, out_channels),
+                Conv(2 * 64, 32),
             ]
         )
         self.upsamplers = nn.ModuleList(
             [Upsample(512), Upsample(256), Upsample(128), Upsample(64)]
         )
 
+        self.out_conv = nn.Conv2d(32, 3, kernel_size=3, padding=1)
+
     def forward(self, x: torch.Tensor, t: torch.Tensor) -> torch.Tensor:
-        B, H, W = x.shape[0], x.shape[2], x.shape[3]
-        t_embedding = self.position_embeddings[t]  # (B, T_DIM)
-        t_embedding = t_embedding.view(B, T_EMBEDDING_SIZE, 1, 1).expand(
-            B, T_EMBEDDING_SIZE, H, W
-        )
-        x = torch.cat((t_embedding, x), axis=1)
+        x = self.preconv(x)
+
+        t_emb = self.position_embeddings[t]  # (B, T_DIM)
 
         intermediates = []
         for enc, dow in zip(self.encoder, self.downsamplers):
-            x = enc(x)
+            x = enc(x, t_emb)
             intermediates.append(x)  # TODO: Is this a copy?
             x = dow(x)
 
-        x = self.bottleneck(x)
+        x = self.bottleneck(x, t_emb)
 
         for dec, up, m in zip(self.decoder, self.upsamplers, reversed(intermediates)):
             x = up(x)
             x = torch.concat((x, m), axis=1)  # Channel dimension
-            x = dec(x)
+            x = dec(x, t_emb)
+
+        x = self.out_conv(x)
 
         return x

src/simple_ddpm/sample.py

@@ -32,15 +32,13 @@ def p_sample(model, x, t, params):
 @torch.no_grad()
 def sample_images(model, image_size, batch_size, channels, device, params):
     """Generate new images using the trained model"""
-    model.eval()
-
-    # Start from pure noise
     x = torch.randn(batch_size, channels, image_size, image_size).to(device)
 
-    # Gradually denoise the image
     for t in tqdm(reversed(range(TIMESTEPS)), desc="Sampling", total=TIMESTEPS):
         t_batch = torch.full((batch_size,), t, device=device, dtype=torch.long)
         x = p_sample(model, x, t_batch, params)
+        if t % 100 == 0:
+            show_images(x)
 
         if x.isnan().any():
             raise ValueError(f"NaN detected in image at timestep {t}")
@@ -54,14 +52,16 @@ def show_images(images, title=""):
         images = images.detach().cpu().numpy()
 
     images = (images * 0.25 + 0.5).clip(0, 1)
-    plt.figure(figsize=(10, 10))
     for idx in range(min(16, len(images))):
         plt.subplot(4, 4, idx + 1)
         plt.imshow(np.transpose(images[idx], (1, 2, 0)))
         plt.axis("off")
     plt.suptitle(title)
-    plt.show()
+    plt.draw()
+    plt.pause(0.001)
+
 
+plt.figure(figsize=(10, 10))
 
 params = get_diffusion_params(TIMESTEPS, device)
 
@@ -78,3 +78,4 @@ generated_images = sample_images(
     params=params,
 )
 show_images(generated_images, title="Generated Images")
+plt.show()

src/simple_ddpm/train.py

@@ -9,12 +9,17 @@ torch.manual_seed(42)
 device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
 
 # Hyperparameters
-NUM_EPOCHS = 128
+NUM_EPOCHS = 256
 BATCH_SIZE = 128
 IMAGE_SIZE = 32
 CHANNELS = 3
 TIMESTEPS = 1000
 
+
+def count_parameters(model):
+    return sum(p.numel() for p in model.parameters() if p.requires_grad)
+
+
 # Data loading and preprocessing
 transform = transforms.Compose(
     [
@@ -31,31 +36,27 @@ train_dataset = datasets.CIFAR10(
 )
 
 train_loader = DataLoader(
-    train_dataset, batch_size=BATCH_SIZE, shuffle=True, num_workers=2, pin_memory=True
+    train_dataset, batch_size=BATCH_SIZE, shuffle=True, num_workers=8, pin_memory=True
 )
 
 
-# Define beta schedule (linear schedule as an example)
 def linear_beta_schedule(timesteps):
     beta_start = 0.0001
     beta_end = 0.02
     return torch.linspace(beta_start, beta_end, timesteps)
 
 
-# Calculate diffusion parameters
 def get_diffusion_params(timesteps, device):
     betas = linear_beta_schedule(timesteps)
     alphas = 1.0 - betas
-    alphas_cumprod = torch.cumprod(alphas, axis=0)
+    alphas_cumprod = torch.cumprod(alphas, dim=0)
     alphas_cumprod_prev = torch.cat([torch.ones(1), alphas_cumprod[:-1]])
 
     sqrt_one_minus_alphas_cumprod = torch.sqrt(1.0 - alphas_cumprod)
 
-    # Calculate posterior mean coefficients
     one_over_alphas = 1.0 / torch.sqrt(alphas)
     posterior_mean_coef = betas / sqrt_one_minus_alphas_cumprod
 
-    # Posterior variance
     posterior_variance = betas * (1.0 - alphas_cumprod_prev) / (1.0 - alphas_cumprod)
 
     return {
@@ -67,7 +68,6 @@ def get_diffusion_params(timesteps, device):
     }
 
 
-# Utility functions
 def extract(a, t, x_shape):
     """Extract coefficients at specified timesteps t"""
     batch_size = t.shape[0]
@@ -75,7 +75,6 @@ def extract(a, t, x_shape):
     return out.reshape(batch_size, *((1,) * (len(x_shape) - 1))).to(t.device)
 
 
-# Training utilities
 def get_loss_fn(model, params):
     def loss_fn(x_0):
         batch_size = x_0.shape[0]
@@ -117,9 +116,8 @@ def train_epoch(model, optimizer, train_loader, loss_fn):
 
 if __name__ == "__main__":
     model = UNet(32, TIMESTEPS).to(device)
-    model_avg = torch.optim.swa_utils.AveragedModel(
-        model, multi_avg_fn=torch.optim.swa_utils.get_ema_multi_avg_fn(0.9999)
-    )
+    nb_params = count_parameters(model)
+    print(f"Total number of parameters: {nb_params}")
     optimizer = torch.optim.AdamW(model.parameters(), lr=1e-4, betas=(0.9, 0.95))
     params = get_diffusion_params(TIMESTEPS, device)
     loss_fn = get_loss_fn(model, params)