Unflatten
class torch.nn.Unflatten(dim, unflattened_size)
Unflattens a tensor dim expanding it to a desired shape. For use
   with "Sequential".


"dim" specifies the dimension of the input tensor to be
     unflattened, and it can be either int or str when Tensor or
     NamedTensor is used, respectively.


"unflattened_size" is the new shape of the unflattened dimension
     of the tensor and it can be a tuple of ints or a list of ints
     or torch.Size for Tensor input;  a NamedShape (tuple of
     (name, size) tuples) for NamedTensor input.


Shape:
      * Input: (, S_{\text{dim}}, ), where S_{\text{dim}} is the
        size at dimension "dim" and * means any number of dimensions
        including none.
  * Output: (*, U_1, ..., U_n, *), where U = "unflattened_size"
    and \prod_{i=1}^n U_i = S_{\text{dim}}.

Parameters:
      * dim (Union[int, str]) -- Dimension to be
        unflattened