docs: def arange_col(n, dtype=int):
      """
      Returns ``np.arange`` in a column form.
      
      :param n: Length of the array.
      :type n: int
      :param dtype: Type of the array.
      :type dtype: type
      :returns: ``np.arange`` in a column form.
      :rtype: ndarray
      """
      return np.reshape(np.arange(n, dtype = dtype), (n, 1))