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Task: cv-diffusion-conditioning

Class-Conditional Diffusion: Conditioning Injection Methods

Background

Class-conditional diffusion models generate images conditioned on a class label. The key design choice is how to inject the class information into the UNet:

  • Cross-Attention: Class embedding serves as key/value in a cross-attention layer after each ResBlock. Used in Stable Diffusion for text conditioning.
  • Adaptive Normalization (AdaLN-Zero): Class embedding modulates LayerNorm with learned scale, shift, and gating parameters. Used in DiT.
  • FiLM Conditioning: Class embedding is added to the timestep embedding and injected via adaptive GroupNorm (scale/shift) in ResBlocks.

Research Question

Which conditioning injection method achieves the best class-conditional FID on CIFAR-10?

Task

You are given custom_train.py, a self-contained class-conditional DDPM training script with a small UNet on CIFAR-10 (32x32, 10 classes).

The editable region contains:

  1. prepare_conditioning(time_emb, class_emb) — controls how class embedding is combined with the timestep embedding before entering ResBlocks.

  2. ClassConditioner(nn.Module) — an additional conditioning module applied after each ResBlock, enabling methods like cross-attention or adaptive norm.

Your goal is to design a conditioning injection method that achieves lower FID than the baselines.

Evaluation

  • Dataset: CIFAR-10 (32x32, 10 classes)
  • Model: UNet2DModel (diffusers backbone) at three scales:
    • Small: block_out_channels=(64,128,128,128), ~9M params, batch 128
    • Medium: block_out_channels=(128,256,256,256), ~36M params, batch 128
    • Large: block_out_channels=(256,512,512,512), ~140M params, batch 64
  • Training: 35000 steps per scale, AdamW lr=2e-4, EMA rate 0.9995
  • Metric: FID (lower is better), computed with clean-fid against CIFAR-10 train set (50k samples)
  • Inference: 50-step DDIM sampling (class-conditional)

Baselines

  1. concat-film: Class embedding added to timestep embedding, injected via FiLM (adaptive GroupNorm) in ResBlocks. Simplest method.
  2. cross-attn: Class embedding used as key/value in cross-attention layers after ResBlocks. Most expressive method.
  3. adanorm: Class embedding generates scale/shift/gate parameters for adaptive LayerNorm after ResBlocks. DiT-style method.

diffusers-main/custom_train.py [EDITABLE — lines 195–227 only]

     1: """Class-Conditional DDPM Training on CIFAR-10.
     2: 
     3: Uses diffusers UNet2DModel backbone (same architecture as google/ddpm-cifar10-32)
     4: with configurable class-conditioning injection. Only the conditioning method
     5: (prepare_conditioning + ClassConditioner) is editable.
     6: """
     7: 
     8: import copy
     9: import math
    10: import os
    11: import sys
    12: import time
    13: 
    14: import numpy as np
    15: import torch
    16: import torch.distributed as dist
    17: import torch.nn 
AssistantStep 1edit
Tool Input
1{
2  "op": "replace",
3  "filename": "diffusers-main/custom_train.py",
4  "start_line": 195,
5  "end_line": 227,
6  "content": "def prepare_conditioning(time_emb, class_emb):\n    \"\"\"Prepare the combined embedding used in ResBlocks.\n\n    TODO: Implement your conditioning preparation here.\n\n    Args:\n        time_emb:  [B, time_embed_dim] timestep embedding\n        class_emb: [B, time_embed_dim] class embedding\n\n    Returns: [B, time_embed_dim] embedding used in ResBlocks\n    \"\"\"\n    # Combined additive and multiplicative conditioning\n    # Simple additive conditioning like concat-film\n    return time_emb + class_emb\n\n\nclass ClassConditioner(nn.Module):\n    \"\"\"Conditioning module applied after each UNet block.\n\n    TODO: Implement your conditioning method here.\n\n    Args (forward):\n        h:         [B, C, H, W] feature map\n        class_emb: [B, time_embed_dim] class embedding\n\n    Available utilities:\n        CrossAttentionLayer(channels, context_dim, num_heads)\n        AdaLNBlock(channels, cond_dim)\n    \"\"\"\n    def __init__(self, channels, cond_dim):\n        super().__init__()\n        # Cross-attention path\n        self.cross_attn = CrossAttentionLayer(channels, cond_dim, num_heads=4)\n        # Adaptive normalization path  \n        self.adaln = AdaLNBlock(channels, cond_dim)\n        # Gating network: produces per-channel weight\n        self.gate_proj = nn.Sequential(\n            nn.SiLU(),\n            nn.Linear(cond_dim, channels)\n        )\n        # Initialize gate output to 0.0 (sigmoid(0.0)=0.5 for equal mixing)\n        nn.init.constant_(self.gate_proj[-1].weight, 0.0)\n        nn.init.constant_(self.gate_proj[-1].bias, 0.0)\n        \n    def forward(self, h, class_emb):\n        attn_out = self.cross_attn(h, class_emb)  # = h + attn_res\n        norm_out = self.adaln(h, class_emb)       # = h + norm_res\n        # Compute gating weights per channel\n        gate = torch.sigmoid(self.gate_proj(class_emb))  # [B, C]\n        gate = gate.view(gate.shape[0], gate.shape[1], 1, 1)  # [B, C, 1, 1]\n        # Combine residuals\n        combined_res = gate * (attn_out - h) + (1 - gate) * (norm_out - h)\n        return h + combined_res"
7}
Tool ResultStep 1
OK: Replaced lines 195..227 with 53 line(s) in diffusers-main/custom_train.py. Editable range: 195–247.

[Current file: diffusers-main/custom_train.py | editable: 195–247 | total: 630 lines]
   192| # Conditioning injection (EDITABLE REGION)
   193| # ============================================================================
   194| 
   195  def prepare_conditioning(time_emb, class_emb):
   196      """Prepare the combined embedding used in ResBlocks.
   197  
   198      TODO: Implement your conditioning preparation here.
   199  
   200      Args:
   201          time_emb:  [B, time_embed_dim] timestep embedding
   202          class_emb: [B, time_embed_dim] class embedding
   203  
   204      Returns: [B, time_embed_dim] embedding used in ResBlocks
   205      """
   206      # Combined additive and multiplicative conditioning
   207      # Simple additive conditioning like concat-film
   208      return time_emb + class_emb
   209  
   210  
   211  class ClassConditioner(nn.Mod
AssistantStep 2test
Tool ResultStep 2
[Test #1] (2 tests remaining; call submit(n=1) to submit this result)

### train_small (scripts/train_small.sh)
Training results:
Model parameters: 10.8M | GPUs: 8
step 200/35000 | loss 0.0349 | 25.7s
step 400/35000 | loss 0.0321 | 24.4s
step 600/35000 | loss 0.0382 | 24.8s
step 800/35000 | loss 0.0270 | 24.2s
step 1000/35000 | loss 0.0401 | 24.7s
step 1200/35000 | loss 0.0334 | 24.5s
step 1400/35000 | loss 0.0317 | 24.9s
step 1600/35000 | loss 0.0228 | 24.7s
step 1800/35000 | loss 0.0323 | 24.5s
step 2000/35000 | loss 0.0434 | 25.4s
step 2200/35000 | loss 0.0429 | 24.5s
step 2400/35000 | loss 0.0275 | 24.7s
step 2600/35000 | loss 0.0466 | 24.7s
step 2800/35000 | loss 0.0285 | 24.7s
step 3000/35000 | loss 0.0348 | 24.7s
step 3200/35000 | loss 0.0347 | 25.2s
step 3400/35000 | loss 0.0325 | 24.3s
step 3600/35000 | loss 0.0300 | 24.3s
step 3800/35000 | loss 0.0354 | 25.3s
step 4000/35000 | loss 0.0228 | 24.8s
step 4200/35000 | loss 0.0346 | 24.8s
step 4400/35000 | loss 0.0205 | 25.3s
step
AssistantStep 3undo
Tool Input
1{
2  "n": 1
3}
Tool ResultStep 3
Undo complete:
Restored: diffusers-main/custom_train.py
AssistantStep 4edit
Tool Input
1{
2  "op": "replace",
3  "filename": "diffusers-main/custom_train.py",
4  "start_line": 195,
5  "end_line": 227,
6  "content": "def prepare_conditioning(time_emb, class_emb):\n    \"\"\"Prepare the combined embedding used in ResBlocks.\n\n    TODO: Implement your conditioning preparation here.\n\n    Args:\n        time_emb:  [B, time_embed_dim] timestep embedding\n        class_emb: [B, time_embed_dim] class embedding\n\n    Returns: [B, time_embed_dim] embedding used in ResBlocks\n    \"\"\"\n    # Simple additive conditioning like concat-film\n    return time_emb + class_emb\n\n\nclass ClassConditioner(nn.Module):\n    \"\"\"Conditioning module applied after each UNet block.\n\n    TODO: Implement your conditioning method here.\n\n    Args (forward):\n        h:         [B, C, H, W] feature map\n        class_emb: [B, time_embed_dim] class embedding\n\n    Available utilities:\n        CrossAttentionLayer(channels, context_dim, num_heads)\n        AdaLNBlock(channels, cond_dim)\n    \"\"\"\n    def __init__(self, channels, cond_dim):\n        super().__init__()\n        # Cross-attention layer\n        self.cross_attn = CrossAttentionLayer(channels, cond_dim, num_heads=4)\n        # Learn per-channel gating weight from class embedding\n        self.gate_proj = nn.Linear(cond_dim, channels)\n        # Initialize zero gate (start with no conditioning, let training learn)\n        nn.init.zeros_(self.gate_proj.weight)\n        nn.init.zeros_(self.gate_proj.bias)\n        \n    def forward(self, h, class_emb):\n        attn_out = self.cross_attn(h, class_emb)  # = h + attn_res\n        # Compute per-channel gate\n        gate = torch.sigmoid(self.gate_proj(class_emb))  # [B, C]\n        gate = gate.view(gate.shape[0], gate.shape[1], 1, 1)\n        # Blend between original h and attn_out\n        # h + gate * (attn_out - h) = (1-gate)*h + gate*attn_out\n        return h + gate * (attn_out - h)"
7}
Tool ResultStep 4
OK: Replaced lines 195..227 with 46 line(s) in diffusers-main/custom_train.py. Editable range: 195–240.

[Current file: diffusers-main/custom_train.py | editable: 195–240 | total: 623 lines]
   192| # Conditioning injection (EDITABLE REGION)
   193| # ============================================================================
   194| 
   195  def prepare_conditioning(time_emb, class_emb):
   196      """Prepare the combined embedding used in ResBlocks.
   197  
   198      TODO: Implement your conditioning preparation here.
   199  
   200      Args:
   201          time_emb:  [B, time_embed_dim] timestep embedding
   202          class_emb: [B, time_embed_dim] class embedding
   203  
   204      Returns: [B, time_embed_dim] embedding used in ResBlocks
   205      """
   206      # Simple additive conditioning like concat-film
   207      return time_emb + class_emb
   208  
   209  
   210  class ClassConditioner(nn.Module):
   211      """Conditioning module applied after each UNet
AssistantStep 5test
Tool ResultStep 5
[Test #2] (1 test remaining; call submit(n=2) to submit this result)

### train_small (scripts/train_small.sh)
Training results:
Model parameters: 10.0M | GPUs: 8
step 200/35000 | loss 0.0350 | 23.2s
step 400/35000 | loss 0.0322 | 22.4s
step 600/35000 | loss 0.0386 | 21.9s
step 800/35000 | loss 0.0272 | 22.7s
step 1000/35000 | loss 0.0406 | 22.1s
step 1200/35000 | loss 0.0334 | 22.3s
step 1400/35000 | loss 0.0320 | 22.5s
step 1600/35000 | loss 0.0230 | 22.0s
step 1800/35000 | loss 0.0321 | 22.0s
step 2000/35000 | loss 0.0430 | 22.2s
step 2200/35000 | loss 0.0429 | 21.9s
step 2400/35000 | loss 0.0276 | 22.1s
step 2600/35000 | loss 0.0471 | 22.5s
step 2800/35000 | loss 0.0284 | 22.0s
step 3000/35000 | loss 0.0346 | 22.1s
step 3200/35000 | loss 0.0347 | 22.3s
step 3400/35000 | loss 0.0324 | 21.9s
step 3600/35000 | loss 0.0304 | 22.0s
step 3800/35000 | loss 0.0355 | 22.5s
step 4000/35000 | loss 0.0226 | 21.9s
step 4200/35000 | loss 0.0346 | 21.8s
step 4400/35000 | loss 0.0207 | 22.2s
step 
AssistantStep 6undo
Tool Input
1{
2  "n": 1
3}
Tool ResultStep 6
Undo complete:
Restored: diffusers-main/custom_train.py
AssistantStep 7edit
Tool Input
1{
2  "op": "replace",
3  "filename": "diffusers-main/custom_train.py",
4  "start_line": 195,
5  "end_line": 227,
6  "content": "def prepare_conditioning(time_emb, class_emb):\n    \"\"\"Prepare the combined embedding used in ResBlocks.\n\n    TODO: Implement your conditioning preparation here.\n\n    Args:\n        time_emb:  [B, time_embed_dim] timestep embedding\n        class_emb: [B, time_embed_dim] class embedding\n\n    Returns: [B, time_embed_dim] embedding used in ResBlocks\n    \"\"\"\n    # Simple additive conditioning like concat-film\n    return time_emb + class_emb\n\n\nclass ClassConditioner(nn.Module):\n    \"\"\"Conditioning module applied after each UNet block.\n\n    TODO: Implement your conditioning method here.\n\n    Args (forward):\n        h:         [B, C, H, W] feature map\n        class_emb: [B, time_embed_dim] class embedding\n\n    Available utilities:\n        CrossAttentionLayer(channels, context_dim, num_heads)\n        AdaLNBlock(channels, cond_dim)\n    \"\"\"\n    def __init__(self, channels, cond_dim):\n        super().__init__()\n        # Adaptive LayerNorm-Zero conditioning\n        self.adaln = AdaLNBlock(channels, cond_dim)\n        # Self-gating: compute per-channel gate from feature map\n        self.self_gate = nn.Sequential(\n            nn.AdaptiveAvgPool2d(1),\n            nn.Conv2d(channels, channels, kernel_size=1),\n            nn.Sigmoid()\n        )\n        # Initialize conv weights zero so initial gate ~0.5\n        nn.init.zeros_(self.self_gate[1].weight)\n        nn.init.zeros_(self.self_gate[1].bias)\n        \n    def forward(self, h, class_emb):\n        # Adaptive normalization output\n        adaln_out = self.adaln(h, class_emb)  # = h + gate * (norm - h)\n        # Compute self-gate from original features\n        gate = self.self_gate(h)  # [B, C, 1, 1]\n        # Blend between original h and conditioned output\n        return h + gate * (adaln_out - h)"
7}
Tool ResultStep 7
OK: Replaced lines 195..227 with 49 line(s) in diffusers-main/custom_train.py. Editable range: 195–243.

[Current file: diffusers-main/custom_train.py | editable: 195–243 | total: 626 lines]
   192| # Conditioning injection (EDITABLE REGION)
   193| # ============================================================================
   194| 
   195  def prepare_conditioning(time_emb, class_emb):
   196      """Prepare the combined embedding used in ResBlocks.
   197  
   198      TODO: Implement your conditioning preparation here.
   199  
   200      Args:
   201          time_emb:  [B, time_embed_dim] timestep embedding
   202          class_emb: [B, time_embed_dim] class embedding
   203  
   204      Returns: [B, time_embed_dim] embedding used in ResBlocks
   205      """
   206      # Simple additive conditioning like concat-film
   207      return time_emb + class_emb
   208  
   209  
   210  class ClassConditioner(nn.Module):
   211      """Conditioning module applied after each UNet
AssistantStep 8test
Tool ResultStep 8
[Test #3] (0 tests remaining)

### train_small (scripts/train_small.sh)
Training results:
Model parameters: 9.9M | GPUs: 8
step 200/35000 | loss 0.0348 | 20.6s
step 400/35000 | loss 0.0320 | 19.8s
step 600/35000 | loss 0.0382 | 20.0s
step 800/35000 | loss 0.0268 | 19.8s
step 1000/35000 | loss 0.0405 | 20.1s
step 1200/35000 | loss 0.0332 | 19.7s
step 1400/35000 | loss 0.0317 | 20.0s
step 1600/35000 | loss 0.0228 | 19.3s
step 1800/35000 | loss 0.0321 | 19.7s
step 2000/35000 | loss 0.0435 | 19.3s
step 2200/35000 | loss 0.0426 | 19.4s
step 2400/35000 | loss 0.0275 | 19.4s
step 2600/35000 | loss 0.0472 | 20.0s
step 2800/35000 | loss 0.0283 | 20.1s
step 3000/35000 | loss 0.0348 | 19.5s
step 3200/35000 | loss 0.0348 | 20.5s
step 3400/35000 | loss 0.0327 | 19.6s
step 3600/35000 | loss 0.0297 | 19.5s
step 3800/35000 | loss 0.0354 | 19.5s
step 4000/35000 | loss 0.0228 | 19.7s
step 4200/35000 | loss 0.0348 | 19.8s
step 4400/35000 | loss 0.0207 | 21.2s
step 4600/35000 | loss 0.0351 | 19.7s
step 48
AssistantStep 1edit
Tool Input
1{
2  "op": "replace",
3  "filename": "diffusers-main/custom_train.py",
4  "start_line": 195,
5  "end_line": 227,
6  "content": "def prepare_conditioning(time_emb, class_emb):\n    \"\"\"Gated cross-attention: additive conditioning in time embedding.\"\"\"\n    return time_emb + class_emb\n\n\nclass ClassConditioner(nn.Module):\n    \"\"\"Gated cross-attention with channel-wise gating.\"\"\"\n    def __init__(self, channels, cond_dim):\n        super().__init__()\n        self.cross_attn = CrossAttentionLayer(channels, cond_dim, num_heads=4)\n        # Gate network: produce per-channel gating scalar\n        self.gate_net = nn.Sequential(\n            nn.SiLU(),\n            nn.Linear(cond_dim, channels)\n        )\n        # Initialize gate output to ~1.0 (bias) so initially cross-attn contributes fully\n        nn.init.zeros_(self.gate_net[-1].weight)\n        nn.init.ones_(self.gate_net[-1].bias)\n\n    def forward(self, h, class_emb):\n        cross_out = self.cross_attn(h, class_emb)\n        # Compute gate per channel, shape [B, C]\n        gate = torch.sigmoid(self.gate_net(class_emb))\n        # Reshape to [B, C, 1, 1] for broadcasting\n        gate = gate.view(gate.shape[0], gate.shape[1], 1, 1)\n        # Blend: h + gate * cross_out\n        return h + gate * cross_out"
7}
Tool ResultStep 1
OK: Replaced lines 195..227 with 27 line(s) in diffusers-main/custom_train.py. Editable range: 195–221.

[Current file: diffusers-main/custom_train.py | editable: 195–221 | total: 604 lines]
   192| # Conditioning injection (EDITABLE REGION)
   193| # ============================================================================
   194| 
   195  def prepare_conditioning(time_emb, class_emb):
   196      """Gated cross-attention: additive conditioning in time embedding."""
   197      return time_emb + class_emb
   198  
   199  
   200  class ClassConditioner(nn.Module):
   201      """Gated cross-attention with channel-wise gating."""
   202      def __init__(self, channels, cond_dim):
   203          super().__init__()
   204          self.cross_attn = CrossAttentionLayer(channels, cond_dim, num_heads=4)
   205          # Gate network: produce per-channel gating scalar
   206          self.gate_net = nn.Sequential(
   207              nn.SiLU(),
   208              nn.Linear(cond_dim, 
AssistantStep 2test