From b480d0cdc21f944e4adccf6e81cc939b0450c5e9 Mon Sep 17 00:00:00 2001
From: YurenHao0426 <Blackhao0426@gmail.com>
Date: Mon, 4 May 2026 19:50:45 -0500
Subject: Initial submission code: FA evaluation protocol + reproduction
 scripts

Reference implementation of the three-diagnostic FA evaluation protocol
(scale stability, reference validity, depth utility) from the NeurIPS 2026
E&D track paper. Includes models, metrics, and full reproduction pipeline.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 models/small_resnet.py | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 models/small_resnet.py

(limited to 'models/small_resnet.py')

diff --git a/models/small_resnet.py b/models/small_resnet.py
new file mode 100644
index 0000000..10b122e
--- /dev/null
+++ b/models/small_resnet.py
@@ -0,0 +1,74 @@
+"""
+Small CIFAR-10 ResNet for the FA-evaluation paper. Standard BatchNorm-based
+post-activation residual blocks (no LayerNorm). 4 residual blocks at width 64.
+
+Supports `num_blocks=0` (shallow baseline: just embed → bn → head) and frozen
+blocks via `requires_grad=False` on `.blocks` parameters.
+"""
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+
+
+class BasicBlock(nn.Module):
+    """Standard ResNet BasicBlock with BatchNorm. Pre-activation NOT used; this is
+    the post-activation form: relu(BN(W2 * relu(BN(W1 x)))) + x. d_hidden in == d_hidden out.
+    No stride / downsampling — all blocks operate at the same spatial resolution
+    after the initial stem. This keeps the architecture simple and matches the
+    "4 residual blocks at fixed width" structure of our ResMLP and ViT-Mini comparisons.
+    """
+    def __init__(self, d_hidden):
+        super().__init__()
+        self.conv1 = nn.Conv2d(d_hidden, d_hidden, kernel_size=3, padding=1, bias=False)
+        self.bn1 = nn.BatchNorm2d(d_hidden)
+        self.conv2 = nn.Conv2d(d_hidden, d_hidden, kernel_size=3, padding=1, bias=False)
+        self.bn2 = nn.BatchNorm2d(d_hidden)
+
+    def forward(self, x):
+        out = F.relu(self.bn1(self.conv1(x)))
+        out = self.bn2(self.conv2(out))
+        out = F.relu(x + out)
+        return out
+
+
+class SmallResNet(nn.Module):
+    """Small CIFAR-10 ResNet:
+        - 3x3 conv stem (3 → d_hidden) + BN + ReLU
+        - num_blocks BasicBlocks at the same width and resolution
+        - global average pool
+        - linear classification head
+
+    `num_blocks=0` gives the shallow baseline (just stem → pool → head).
+    """
+    def __init__(self, d_hidden=64, num_classes=10, num_blocks=4):
+        super().__init__()
+        self.stem_conv = nn.Conv2d(3, d_hidden, kernel_size=3, padding=1, bias=False)
+        self.stem_bn = nn.BatchNorm2d(d_hidden)
+        self.blocks = nn.ModuleList([BasicBlock(d_hidden) for _ in range(num_blocks)])
+        self.out_head = nn.Linear(d_hidden, num_classes)
+        self.num_blocks = num_blocks
+        self.d_hidden = d_hidden
+
+    def stem(self, x):
+        # x: (B, 3, 32, 32)
+        if x.dim() == 2:
+            x = x.view(x.size(0), 3, 32, 32)
+        h = F.relu(self.stem_bn(self.stem_conv(x)))
+        return h
+
+    def forward(self, x, return_hidden=False):
+        h = self.stem(x)                      # (B, d, 32, 32)
+        hiddens = [h] if return_hidden else None
+        for block in self.blocks:
+            h = block(h)
+            if return_hidden:
+                hiddens.append(h)
+        h_pool = F.adaptive_avg_pool2d(h, 1).flatten(1)   # (B, d)
+        logits = self.out_head(h_pool)
+        if return_hidden:
+            return logits, hiddens
+        return logits
+
+    # Convenience alias for snapshot script compatibility (treats stem as the embed)
+    def embed(self, x):
+        return self.stem(x)
-- 
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