one can pass a callback to token_dropout_prob for NaViT that takes in…

… height and width and calculate appropriate dropout rate

setup.py

@@ -3,7 +3,7 @@
 setup(
   name = 'vit-pytorch',
   packages = find_packages(exclude=['examples']),
-  version = '1.2.7',
+  version = '1.2.8',
   license='MIT',
   description = 'Vision Transformer (ViT) - Pytorch',
   long_description_content_type = 'text/markdown',

vit_pytorch/na_vit.py

@@ -138,14 +138,25 @@ def forward(
         return self.norm(x)
 
 class NaViT(nn.Module):
-    def __init__(self, *, image_size, patch_size, num_classes, dim, depth, heads, mlp_dim, channels = 3, dim_head = 64, dropout = 0., emb_dropout = 0., token_dropout_prob = 0.):
+    def __init__(self, *, image_size, patch_size, num_classes, dim, depth, heads, mlp_dim, channels = 3, dim_head = 64, dropout = 0., emb_dropout = 0., token_dropout_prob = None):
         super().__init__()
         image_height, image_width = pair(image_size)
 
         # what percent of tokens to dropout
-        # in paper, they found this should vary depending on resolution (todo - figure out how to do this, maybe with callback?)
+        # if int or float given, then assume constant dropout prob
+        # otherwise accept a callback that in turn calculates dropout prob from height and width
 
-        self.token_dropout_prob = token_dropout_prob
+        self.calc_token_dropout = calc_token_dropout = None
+
+        if callable(token_dropout_prob):
+            self.calc_token_dropout = token_dropout_prob
+
+        elif isinstance(token_dropout_prob, (float, int)):
+            assert 0. < token_dropout_prob < 1.
+            token_dropout_prob = float(token_dropout_prob)
+            self.calc_token_dropout = lambda height, width: token_dropout_prob
+
+        # calculate patching related stuff
 
         assert divisible_by(image_height, patch_size) and divisible_by(image_width, patch_size), 'Image dimensions must be divisible by the patch size.'
 
@@ -190,7 +201,7 @@ def forward(
         self,
         batched_images: List[List[Tensor]] # assume different resolution images already grouped correctly
     ):
-        p, c, device, has_token_dropout = self.patch_size, self.channels, self.device, self.token_dropout_prob > 0.
+        p, c, device, has_token_dropout = self.patch_size, self.channels, self.device, exists(self.calc_token_dropout)
 
         arange = partial(torch.arange, device = device)
         pad_sequence = partial(orig_pad_sequence, batch_first = True)
@@ -227,8 +238,10 @@ def forward(
                 seq_len = seq.shape[-2]
 
                 if has_token_dropout:
-                    num_keep = max(1, int(seq_len * (1 - self.token_dropout_prob)))
+                    token_dropout = self.calc_token_dropout(*image_dims)
+                    num_keep = max(1, int(seq_len * (1 - token_dropout)))
                     keep_indices = torch.randn((seq_len,), device = device).topk(num_keep, dim = -1).indices
+
                     seq = seq[keep_indices]
                     pos = pos[keep_indices]