Ok, this is what I did :
Q = 2ia(P + 2q) , P = \frac{p-iaq}{2ia}
which means that Q and p are independent coordintes, which means the generating function will be of the third kind, F_3(Q,p) .
for the third kind,
q = -\frac{\partial F_3}{\partial p} = \frac{p}{ia}-2P
P = -\frac{\partial...