Function File: qdot = diff (q, omega)

Derivative of a quaternion.

Let Q be a quaternion to transform a vector from a fixed frame to a rotating frame. If the rotating frame is rotating about the [x, y, z] axes at angular rates [wx, wy, wz], then the derivative of Q is given by

          Q' = diff(Q, omega)

If the passive convention is used (rotate the frame, not the vector), then

          Q' = diff(Q,-omega)