Thank you very much, I understand,
But for lighting reflector design, I still need parabolic curve(rhino.geometry,parabolar),
Changing parameter(focus length and its position and curve ends, but still parabolic curve), designer finds best surface to send lights where he want to aim. Especially for Automotive Headlamp Reflector Design, it is necessary.
Anyway Catia and Solidworks API have all kind of curve function individually which their sketch method supports.
I'm not so good at Nurbs, so I have to study how to draw parabolic curve using nurbs(in rhino common).
But it will be very difficult way for me that maintaining curve entity(parabolic as paraboic), and being able to find focus position,and modifying curve to achieve satisfying curve and surface.
I also hope Curve fuction using 'function' (such as y=x^2+2, start x is 0, end x is 5), which Solidworks API now supports. not far until Rhino6, I hope in Rhino5.