Function that converts a list of tensors corresponding to a structure
    and returns a dictionary consisting of unique tensor keys with symmop
    values corresponding to transformations that will result in derivative
    tensors from the original list

    Args:
        tensors (list of tensors): list of Tensor objects to test for
            symmetrically-equivalent duplicates
        structure (Structure): structure from which to get symmetry
        tol (float): tolerance for tensor equivalence
        kwargs: keyword arguments for the SpacegroupAnalyzer

    returns:
        dictionary consisting of unique tensors with symmetry operations
        corresponding to those which will reconstruct the remaining
        tensors as values

def symmetry_reduce(tensors, structure, tol=1e-8, **kwargs):
    """
    Function that converts a list of tensors corresponding to a structure
    and returns a dictionary consisting of unique tensor keys with symmop
    values corresponding to transformations that will result in derivative
    tensors from the original list

    Args:
        tensors (list of tensors): list of Tensor objects to test for
            symmetrically-equivalent duplicates
        structure (Structure): structure from which to get symmetry
        tol (float): tolerance for tensor equivalence
        kwargs: keyword arguments for the SpacegroupAnalyzer

    returns:
        dictionary consisting of unique tensors with symmetry operations
        corresponding to those which will reconstruct the remaining
        tensors as values
    """
    sga = SpacegroupAnalyzer(structure, **kwargs)
    symmops = sga.get_symmetry_operations(cartesian=True)
    unique_mapping = TensorMapping([tensors[0]], [[]], tol=tol)
    for tensor in tensors[1:]:
        is_unique = True
        for unique_tensor, symmop in itertools.product(unique_mapping, symmops):
            if np.allclose(unique_tensor.transform(symmop), tensor, atol=tol):
                unique_mapping[unique_tensor].append(symmop)
                is_unique = False
                break
        if is_unique:
            unique_mapping[tensor] = []
    return unique_mapping