fix t2t vit having two layernorms, and make final layernorm in distillation wrapper configurable, default to False for vit

Author: lucidrains

setup.py

@@ -6,7 +6,7 @@
 setup(
   name = 'vit-pytorch',
   packages = find_packages(exclude=['examples']),
-  version = '1.6.9',
+  version = '1.7.0',
   license='MIT',
   description = 'Vision Transformer (ViT) - Pytorch',
   long_description=long_description,

vit_pytorch/distill.py

@@ -1,6 +1,8 @@
 import torch
-import torch.nn.functional as F
 from torch import nn
+from torch.nn import Module
+import torch.nn.functional as F
+
 from vit_pytorch.vit import ViT
 from vit_pytorch.t2t import T2TViT
 from vit_pytorch.efficient import ViT as EfficientViT
@@ -12,6 +14,9 @@
 def exists(val):
     return val is not None
 
+def default(val, d):
+    return val if exists(val) else d
+
 # classes
 
 class DistillMixin:
@@ -20,12 +25,12 @@ def forward(self, img, distill_token = None):
         x = self.to_patch_embedding(img)
         b, n, _ = x.shape
 
-        cls_tokens = repeat(self.cls_token, '() n d -> b n d', b = b)
+        cls_tokens = repeat(self.cls_token, '1 n d -> b n d', b = b)
         x = torch.cat((cls_tokens, x), dim = 1)
         x += self.pos_embedding[:, :(n + 1)]
 
         if distilling:
-            distill_tokens = repeat(distill_token, '() n d -> b n d', b = b)
+            distill_tokens = repeat(distill_token, '1 n d -> b n d', b = b)
             x = torch.cat((x, distill_tokens), dim = 1)
 
         x = self._attend(x)
@@ -97,15 +102,16 @@ def _attend(self, x):
 
 # knowledge distillation wrapper
 
-class DistillWrapper(nn.Module):
+class DistillWrapper(Module):
     def __init__(
         self,
         *,
         teacher,
         student,
         temperature = 1.,
         alpha = 0.5,
-        hard = False
+        hard = False,
+        mlp_layernorm = False
     ):
         super().__init__()
         assert (isinstance(student, (DistillableViT, DistillableT2TViT, DistillableEfficientViT))) , 'student must be a vision transformer'
@@ -122,14 +128,14 @@ def __init__(
         self.distillation_token = nn.Parameter(torch.randn(1, 1, dim))
 
         self.distill_mlp = nn.Sequential(
-            nn.LayerNorm(dim),
+            nn.LayerNorm(dim) if mlp_layernorm else nn.Identity(),
             nn.Linear(dim, num_classes)
         )
 
     def forward(self, img, labels, temperature = None, alpha = None, **kwargs):
-        b, *_ = img.shape
-        alpha = alpha if exists(alpha) else self.alpha
-        T = temperature if exists(temperature) else self.temperature
+
+        alpha = default(alpha, self.alpha)
+        T = default(temperature, self.temperature)
 
         with torch.no_grad():
             teacher_logits = self.teacher(img)

vit_pytorch/t2t.py

@@ -61,10 +61,7 @@ def __init__(self, *, image_size, num_classes, dim, depth = None, heads = None,
         self.pool = pool
         self.to_latent = nn.Identity()
 
-        self.mlp_head = nn.Sequential(
-            nn.LayerNorm(dim),
-            nn.Linear(dim, num_classes)
-        )
+        self.mlp_head = nn.Linear(dim, num_classes)
 
     def forward(self, img):
         x = self.to_patch_embedding(img)