[Nek5000-users] how to define boundary conditions with a specified function.

[nek5000-users at lists.mcs.anl.gov]

Hello everyone,
Now I have a problem.  that how to define boundary conditions in the .usr file.
I know that I can write some code in the usrbc()

what I want do is like this

if (y .eq. 1) then
	u=2*x
endif
where y is the value of boundary coodinates .

what I wrote is like
if (ym1(1,1,11) .eq. 1) then
	ux=2*x
	uy=0
	uz=0
endif

it can be compiled, but not imposed. so what should I do? How can I know the relation between ux(i,j,k,e) and index informations? thanks.

Wei