Height map based on gradient.

Hello,

I am just getting into grasshopper and first time on this board.  Lots of great information.  I am trying to figure out how to change the z-scale on a grid of boxes using a circle gradient to gradually raise from center out.   I was able to get the random to work for another design I was doing but am trying to figure out how to use gradient maps or even sin waves for height.   

I'm not the greatest programmer and know just enough to break things.   

Does anyone have any insight on this?  I attached a grab of where I'm at now.   

Thank you.