I changed hidden to
hidden = torch.cat(torch.randn(1, 48, 128), torch.randn(1, 48, 128))

and I get the following error
Traceback (most recent call last):
  File "lstm.py", line 95, in <module>
    hidden = torch.cat(torch.randn(1, 48, 128), torch.randn(1, 48, 128))
TypeError: cat(): argument 'tensors' (position 1) must be tuple of Tensors, not Tensor