[Fix] fix issue related bugs (open-mmlab#161)

* [Fix] fix version check of pytorch

* [Fix] fix data format in simclr

mmselfsup/datasets/builder.py

@@ -103,7 +103,7 @@ def build_dataloader(dataset,
         worker_init_fn, num_workers=num_workers, rank=rank,
         seed=seed) if seed is not None else None
 
-    if digit_version(torch.__version__) >= digit_version('1.7.0'):
+    if digit_version(torch.__version__) >= digit_version('1.8.0'):
         kwargs['persistent_workers'] = persistent_workers
 
     if kwargs.get('prefetch') is not None:

mmselfsup/models/algorithms/simclr.py

@@ -69,7 +69,9 @@ def forward_train(self, img, **kwargs):
             dict[str, Tensor]: A dictionary of loss components.
         """
         assert isinstance(img, list)
-        img = torch.cat(img)
+        img = torch.stack(img, 1)
+        img = img.reshape(
+            (img.size(0) * 2, img.size(2), img.size(3), img.size(4)))
         x = self.extract_feat(img)  # 2n
         z = self.neck(x)[0]  # (2n)xd
         z = z / (torch.norm(z, p=2, dim=1, keepdim=True) + 1e-10)