As shown in the following experiment, the default dim is 0 for the tensor view while the default dim is 1 for the original tensor. A discussion 126 about dim at Stack Overflow might help you.
>>> import torch
>>> import torch.nn.functional as F
>>> v = torch.randn(1, 2, 2, 2)
>>> F.softmax(v)
__main__:1: UserWarning: Implicit dimension choice for softmax has been deprecated. Change the call to include dim=X as an argument.
tensor([[[[0.1006, 0.1361],
          [0.2072, 0.8304]],

         [[0.8994, 0.8639],
          [0.7928, 0.1696]]]])
>>> F.softmax(v, dim=0)
tensor([[[[1., 1.],
          [1., 1.]],

         [[1., 1.],
          [1., 1.]]]])
>>> F.softmax(v, dim=1)
tensor([[[[0.1006, 0.1361],
          [0.2072, 0.8304]],

         [[0.8994, 0.8639],
          [0.7928, 0.1696]]]])
>>> F.softmax(v, dim=2)
tensor([[[[0.0313, 0.2495],
          [0.9687, 0.7505]],

         [[0.0701, 0.9117],
          [0.9299, 0.0883]]]])
>>> F.softmax(v, dim=3)
tensor([[[[0.0993, 0.9007],
          [0.5318, 0.4682]],

         [[0.1345, 0.8655],
          [0.9551, 0.0449]]]])
>>> w = v.view(1,2,4)
>>> F.softmax(w)
tensor([[[1., 1., 1., 1.],
         [1., 1., 1., 1.]]])
>>> F.softmax(w, dim=0)
tensor([[[1., 1., 1., 1.],
         [1., 1., 1., 1.]]])
>>> F.softmax(w, dim=1)
tensor([[[0.1006, 0.1361, 0.2072, 0.8304],
         [0.8994, 0.8639, 0.7928, 0.1696]]])
>>> F.softmax(w, dim=2)
tensor([[[0.0146, 0.1327, 0.4535, 0.3992],
         [0.0469, 0.3019, 0.6220, 0.0292]]])