From ad557695cccdcdc679194f3ec88c0e30ff0b8596 Mon Sep 17 00:00:00 2001
From: YurenHao0426 <Blackhao0426@gmail.com>
Date: Mon, 27 Jul 2026 14:17:11 -0500
Subject: baseline: add matched Transformer PEPITA

---
 experiments/transformer_feedback_smoke.py | 75 +++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

(limited to 'experiments/transformer_feedback_smoke.py')

diff --git a/experiments/transformer_feedback_smoke.py b/experiments/transformer_feedback_smoke.py
index c3cd4da..1e27b38 100644
--- a/experiments/transformer_feedback_smoke.py
+++ b/experiments/transformer_feedback_smoke.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 """Deterministic audits for Transformer BP/FA/KP/SDIL feedback transport."""
 import json
+import math
 import os
 import sys
 
@@ -245,6 +246,79 @@ def audit_strict_dfa():
     }
 
 
+def audit_pepita():
+    config = LocalTransformerConfig(
+        vocab_size=13, context_length=6, depth=2, width=8, heads=2,
+        mlp_ratio=2, seed=141)
+    bp = LocalDecoderTransformer(config, "bp", dtype=torch.float64)
+    pepita = LocalDecoderTransformer(config, "pepita", dtype=torch.float64)
+    generator = torch.Generator().manual_seed(142)
+    tokens = torch.randint(0, 13, (3, 6), generator=generator)
+    targets = torch.randint(0, 13, (3, 6), generator=generator)
+    with torch.no_grad():
+        bp_output = bp(tokens)["logits"]
+        clean = pepita(tokens, return_cache=True)
+        one_hot = torch.nn.functional.one_hot(
+            targets, 13).to(torch.float64)
+        clean_error = torch.softmax(clean["logits"], dim=-1) - one_hot
+        offset = clean_error @ pepita.pepita_input_feedback
+        modulated = pepita(
+            tokens, return_cache=True, embedding_offset=offset)
+        modulated_error = (
+            torch.softmax(modulated["logits"], dim=-1) - one_hot)
+    forward_error = float(torch.max(torch.abs(
+        bp_output - clean["logits"])))
+    feedback_before = pepita.pepita_input_feedback.detach().clone()
+    metrics = pepita.pepita_gradients(tokens, targets)
+    missing = [
+        name for name, parameter in pepita.named_parameters()
+        if parameter.grad is None]
+    nonfinite = [
+        name for name, parameter in pepita.named_parameters()
+        if parameter.grad is not None
+        and not torch.isfinite(parameter.grad).all()]
+    observations = targets.numel()
+    expected_head = (
+        (modulated_error / observations).reshape(-1, 13).t()
+        @ modulated["normalized"].reshape(-1, 8))
+    head_error = _relative_error(
+        pepita.head.weight.grad, expected_head)
+    embedding_field = clean["embedded"] - modulated["embedded"]
+    expected_position = embedding_field.sum(dim=0) / observations
+    position_error = _relative_error(
+        pepita.position_embedding.grad[:tokens.shape[1]],
+        expected_position)
+    feedback_change = float(torch.max(torch.abs(
+        pepita.pepita_input_feedback - feedback_before)))
+    projection_limit = math.sqrt(6.0 / config.width) * 0.05
+    observed_limit = float(torch.max(torch.abs(
+        pepita.pepita_input_feedback)))
+    if (forward_error >= 1e-12 or head_error >= 1e-12
+            or position_error >= 1e-12 or feedback_change != 0.0
+            or observed_limit > projection_limit or missing or nonfinite):
+        raise AssertionError({
+            "forward_error": forward_error,
+            "head_error": head_error,
+            "position_error": position_error,
+            "feedback_change": feedback_change,
+            "projection_limit": projection_limit,
+            "observed_limit": observed_limit,
+            "missing": missing,
+            "nonfinite": nonfinite,
+        })
+    return {
+        "matched_forward_max_absolute_error": forward_error,
+        "head_local_equation_relative_error": head_error,
+        "position_local_equation_relative_error": position_error,
+        "fixed_projection_change": feedback_change,
+        "projection_limit": projection_limit,
+        "observed_projection_max": observed_limit,
+        "training_presentations": metrics["training_presentations"],
+        "detached_block_boundaries": metrics["detached_block_boundaries"],
+        "uses_task_loss_backward": metrics["uses_task_loss_backward"],
+    }
+
+
 def main():
     torch.set_num_threads(1)
     result = {
@@ -254,6 +328,7 @@ def main():
             audit_fa_independence_and_kp_locality(),
         "sdil_innovation_identity": audit_sdil_innovation_identity(),
         "strict_dfa": audit_strict_dfa(),
+        "pepita": audit_pepita(),
     }
     print(json.dumps(result, indent=2, sort_keys=True))
 
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