fix: correct the positional encoding of Transformer in pytorch examples

Author: Galaxy-Husky

src/lightning/pytorch/demos/transformer.py

@@ -88,7 +88,7 @@ def forward(self, x: Tensor) -> Tensor:
             # TODO: Could make this a `nn.Parameter` with `requires_grad=False`
             self.pe = self._init_pos_encoding(device=x.device)
 
-        x = x + self.pe[: x.size(0), :]
+        x = x + self.pe[:, x.size(1)]
         return self.dropout(x)
 
     def _init_pos_encoding(self, device: torch.device) -> Tensor:
@@ -97,7 +97,7 @@ def _init_pos_encoding(self, device: torch.device) -> Tensor:
         div_term = torch.exp(torch.arange(0, self.dim, 2, device=device).float() * (-math.log(10000.0) / self.dim))
         pe[:, 0::2] = torch.sin(position * div_term)
         pe[:, 1::2] = torch.cos(position * div_term)
-        pe = pe.unsqueeze(0).transpose(0, 1)
+        pe = pe.unsqueeze(0)
         return pe