How to represent circuit in state space
it's depend on your output y. If you take U = V(t) and Y= Vout = V(R2)+V(C2)=V(R3)+V(C3);
than we have:
dX/dt = A* X + BU
Y=CX+D*U
Equations:
V(t) = U = R1*I1+Zeq*I1 with Zeq = (R2+1/JC1W)//(R3+1/JC2W)
Y(t) = Vout = Zeq *I1
Y(t)/U(t)= Zeq/(Zeq+R1)
Y(t)/U(t) = 1/(R1/Zeq+1)
Y(t) + (R1/Zeq+1) * Y(t) = U(t) with s=jw;
you will get dY/dt = A* Y(t) + B* U(t)
and Y(t) = C* Y(t) with C =1 (first order).