For subsonic flow, Eq. 11 12 is an elliptic partial differential equation. For supersonic flow, Eq 11 12 is a hyperbolic partial differential equation. For transonic flow, Eq 11 12 is mixed type equationFor subsonic flow, Eq. 11.12 is an elliptic partial differential equation. For supersonic flow, Eq.11.12 is a hyperbolic partial differential equation. For transonic flow, Eq.11.12 is mixed type equation