How to make transparency gradient in Arnold?

[Anonymous]

Hi I'm using arnold, and I need to make transparent texture, but it should have gradient. 

So, it should non transparent in the bottom, but it becomes transparent going to top.

But I don't know how to make transparency gradient. 

Does anyone know how to do this?

Thank you

[Stephen.Blair]

Ramp shader, plugged into Opacity of Standard Surface

Opaque disabled on object