'''
.. todo::

    Add a modulus_squared function.
'''

import math


def sum_diff(a, b):
    '''
    Calculate the sum and the difference of two variables.

    :param a: number
    :param b: number

    :return sum: sum of *a* and *b*
    :return diff: difference between *a* and *b*

    ::

        # Examples
        sum(1, 3) # output 4, -2
        sum(1+1j, -1j) # output 1, 1+2j
    '''
    sum = a + b
    diff = a - b
    return sum, diff


def modulus(z):
    r'''
    Calculate the modulus :math:`|z|` of a complex number :math:`z`.
    The modulus is given by:

    .. math::

        |z| = \sqrt{[\Re(z)]^2+[\Im(z)]^2}

    :param z: complex number

    :return modulus: modulus of :math:`z`
    '''
    modulus = math.sqrt(z.real**2 + z.imag**2)
    return modulus

.. todo::

     Things to be done.

.. note::

     Some notes.

::

     # python code
    

In the text :math:`x+y`, like $x+y$ in latex

.. math::

     x+y

like $$x+y$$ in latex