Question: mathmatic formulation of a horn

Hello, Is there a mathmatical formula for horn 3D plot simulation. I tried the following but no luck so far. http://en.wikipedia.org/wiki/Cylindrical_coordinates http://mathworld.wolfram.com/Cone.html How do I convet a cone formula to a Horn formula. Where I can control the shape and size of the horn using parameters. I any help would be appreciated. Regards Raj
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