> I've only just started using Maxima so please bear with me:
No problem -- this is a very common difficulty people have with Maxima.
Fortunately, the solution is very simple.
Instead of:
> plot2d(s(x),[x,-8,8]);
use
plot2d('(s(x)),[x,-8,8]);
The problem is that Maxima is trying to evaluate its first argument for
a symbolic 'x'. This is so that you can say things like
plot2d(diff(f(x),x),...)
or
plot2d(d4, ...)
or whatever.
The solution is to quote the argument when do not want it evaluated this
way.
I would normally suggest that you analyze this expression symbolically,
except that Maxima is currently rather weak on simplifying expressions
using signum and entier. (I am working on this.)
Don't hesitate to ask other questions!
-s