feat(pusht): add dual-head uv transformer

diffusion_policy/model/diffusion/pmf_transformer_for_diffusion.py

@@ -27,6 +27,7 @@ class PMFTransformerForDiffusion(ModuleAttrMixin):
         obs_as_cond: bool = False,
         n_cond_layers: int = 0,
         n_time_tokens: int = 4,
+        n_head_layers: int = 4,
     ) -> None:
         super().__init__()
 
@@ -34,11 +35,18 @@ class PMFTransformerForDiffusion(ModuleAttrMixin):
             n_obs_steps = horizon
         if n_time_tokens < 1:
             raise ValueError("n_time_tokens must be >= 1")
+        if n_head_layers < 0:
+            raise ValueError("n_head_layers must be >= 0")
+        if n_head_layers >= n_layer:
+            raise ValueError(
+                "n_head_layers must be smaller than n_layer so shared trunk depth stays positive"
+            )
 
         obs_as_cond = cond_dim > 0
         T = horizon
         n_global_cond_tokens = 2 * n_time_tokens
         T_cond = n_global_cond_tokens + (n_obs_steps if obs_as_cond else 0)
+        n_shared_layers = n_layer - n_head_layers
 
         self.input_emb = nn.Linear(input_dim, n_emb)
         self.pos_emb = nn.Parameter(torch.zeros(1, T, n_emb))
@@ -81,9 +89,17 @@ class PMFTransformerForDiffusion(ModuleAttrMixin):
             batch_first=True,
             norm_first=True,
         )
-        self.decoder = nn.TransformerDecoder(
+        self.shared_decoder = nn.TransformerDecoder(
             decoder_layer=decoder_layer,
-            num_layers=n_layer,
+            num_layers=n_shared_layers,
+        )
+        self.u_decoder = nn.TransformerDecoder(
+            decoder_layer=decoder_layer,
+            num_layers=n_head_layers,
+        )
+        self.v_decoder = nn.TransformerDecoder(
+            decoder_layer=decoder_layer,
+            num_layers=n_head_layers,
         )
 
         if causal_attn:
@@ -109,7 +125,8 @@ class PMFTransformerForDiffusion(ModuleAttrMixin):
             self.mask = None
             self.memory_mask = None
 
-        self.ln_f = nn.LayerNorm(n_emb)
+        self.ln_u = nn.LayerNorm(n_emb)
+        self.ln_v = nn.LayerNorm(n_emb)
         self.head_u = nn.Linear(n_emb, output_dim)
         self.head_v = nn.Linear(n_emb, output_dim)
 
@@ -120,11 +137,20 @@ class PMFTransformerForDiffusion(ModuleAttrMixin):
         self.obs_as_cond = obs_as_cond
         self.n_global_cond_tokens = n_global_cond_tokens
         self.n_time_tokens = n_time_tokens
+        self.n_layer = n_layer
+        self.n_head_layers = n_head_layers
+        self.n_shared_layers = n_shared_layers
 
         self.apply(self._init_weights)
         logger.info(
             "number of parameters: %e", sum(p.numel() for p in self.parameters())
         )
+        logger.info(
+            "PMFTransformerForDiffusion layers: shared=%d u_head=%d v_head=%d",
+            self.n_shared_layers,
+            self.n_head_layers,
+            self.n_head_layers,
+        )
 
     def _init_weights(self, module):
         ignore_types = (
@@ -255,11 +281,22 @@ class PMFTransformerForDiffusion(ModuleAttrMixin):
 
         token_pos = self.pos_emb[:, : input_emb.shape[1], :]
         x = self.drop(input_emb + token_pos)
-        x = self.decoder(
+        shared_x = self.shared_decoder(
             tgt=x,
             memory=memory,
             tgt_mask=self.mask,
             memory_mask=self.memory_mask,
         )
-        x = self.ln_f(x)
-        return self.head_u(x), self.head_v(x)
+        u_x = self.u_decoder(
+            tgt=shared_x,
+            memory=memory,
+            tgt_mask=self.mask,
+            memory_mask=self.memory_mask,
+        )
+        v_x = self.v_decoder(
+            tgt=shared_x,
+            memory=memory,
+            tgt_mask=self.mask,
+            memory_mask=self.memory_mask,
+        )
+        return self.head_u(self.ln_u(u_x)), self.head_v(self.ln_v(v_x))

diffusion_policy/policy/pmf_transformer_hybrid_image_policy.py

@@ -42,6 +42,7 @@ class PMFTransformerHybridImagePolicy(BaseImagePolicy):
         obs_as_cond=True,
         pred_action_steps_only=False,
         n_time_tokens=4,
+        n_head_layers=4,
         min_time=0.05,
         du_dt_epsilon=1.0e-3,
         pmf_u_loss_weight=1.0,
@@ -155,6 +156,7 @@ class PMFTransformerHybridImagePolicy(BaseImagePolicy):
             obs_as_cond=obs_as_cond,
             n_cond_layers=n_cond_layers,
             n_time_tokens=n_time_tokens,
+            n_head_layers=n_head_layers,
         )
         self.noise_scheduler = noise_scheduler
         self.mask_generator = LowdimMaskGenerator(

image_pusht_diffusion_policy_dit_pmf.yaml

@@ -63,6 +63,7 @@ policy:
   n_emb: 256
   n_head: 4
   n_layer: 12
+  n_head_layers: 4
   n_obs_steps: 2
   n_time_tokens: 4
   noise_scale: 1.0