functions

Hi,

 I am using Abaqus/CAE to model the elastic behaviour of a plate. I would like to give/define a function to prescribe the displacement along one boundary, but Abaqus does not seem to accept this the way I'm doing it*. Can anyone help me out?

* on the Load module, I choose create boundary condition > displacement, then I select a boundary, select distribution user defined, and on u1 i type "x". I then get a message saying this is not accepted.