def generate_inverse(conversions):
    """Generate all simple inverse conversions.

    A simple inverse conversion is something we can obtain by doing
    a ``1 / unit`` type of conversion.

    Parameters
    ----------
    conversions : dictionary
        The unit conversions, assumed to be of type `convert[quantity]`.
        Note that this variable will be updated by this function.

    Returns
    -------
    out : None
        Will not return anything, but will update the given parameter
        `conversions`.
    """
    newconvert = {}
    for unit in conversions:
        unit_from, unit_to = unit
        newunit = unit_to, unit_from
        if newunit not in conversions:
            newconvert[newunit] = 1.0 / conversions[unit]
    for newunit in newconvert:
        conversions[newunit] = newconvert[newunit]
