I want to define a rough wall by using wall/lj93 command including a sinusoidal function for the wall (ZRough) as a function of x coordinate like:

variable ZRough equal “sin(2PIv_x)”

But I couldn’t find anything in the documentation and mailing list showing how to define a position variable for x direction to use as “v_x” in the above formula. Moreover, my wall/lj93 command line is:

fix walllo all wall/lj93 zlo ${ZRough} 0.42 1.122 50.0 units box

I was wondering if somebody could help me with this issue?

I want to define a rough wall by using wall/lj93 command including a
sinusoidal function for the wall (ZRough) as a function of x coordinate
like:

variable ZRough equal "sin(2*PI*v_x)"

But I couldn't find anything in the documentation and mailing list showing
how to define a position variable for x direction to use as "v_x" in the
above formula. Moreover, my wall/lj93 command line is:

fix walllo all wall/lj93 zlo ${ZRough} 0.42 1.122 50.0 units box

I was wondering if somebody could help me with this issue?

if the documentation does say that you can do it, then you cannot do it.
if you want a wall that is not flat, you will have to write a new
fix.style or approximate it with immobile particles.

So isn't there a way to define the global x coordinate?

which part of "if you want a wall that is not flat, you will have to
write a new
fix.style or approximate it with immobile particles" did you not understand?