[ 0.5348,  0.0634, -2.0494],
                               [-0.7125, -1.0646,  2.1844]],

                              [[ 0.1276,  0.1874, -0.6334],
                               [-1.9682, -0.5340,  0.7483]]]),
               size=(5, 5, 2, 3), nnz=3, layout=torch.sparse_coo)

        # when sum over only part of sparse_dims, return a sparse tensor
        >>> torch.sparse.sum(S, [1, 3])
        tensor(indices=tensor([[0, 2, 3]]),
               values=tensor([[-1.4512,  0.4073],
                              [-0.8901,  0.2017],
                              [-0.3183, -1.7539]]),
               size=(5, 2), nnz=3, layout=torch.sparse_coo)

        # when sum over all sparse dim, return a dense tensor
        # with summed dims squeezed
        >>> torch.sparse.sum(S, [0, 1, 3])
        tensor([-2.6596, -1.1450])
    N)