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

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))