atan
====

.. qcs:function:: atan (y, [x])
    :category: math

    :param y: Value representing the proportion of the y-coordinate.
    :type y: :qcs:type:`series` or :qcs:type:`numeric`

    :param x: Value representing the proportion of the x-coordinate. Default value is **1**.
    :type x: :qcs:type:`series` or :qcs:type:`numeric`

    :returns: same type as **y**

    Returns the arc tangent of :math:`\frac{y}{x}` in radians in 
    the range :math:`[-\frac{\pi}{2},\frac{\pi}{2}]`