def list_add(lists_of_lists):
    """Element-wise sum of list of lists

    Parameters
    ----------
    lists_of_lists: list
        List of numbers

    Returns
    -------
    list
    """
    assert len(lists_of_lists) > 0
    new_ls = [0] * len(lists_of_lists[0])
    for sublist in lists_of_lists:
        for i, elem in enumerate(sublist):
            new_ls[i] += elem
    return new_ls