> Do you see a possibility to not get the graph go down to x-axis?
If the function returns a symbol rather than a number, plot will not
plot any points. For example:
f(x):= if x<0 then sin(x) else if x>1 then cos(x) else 'foo;
plot2d('(f(x)),[x,-1,2]);
I think this is what you want.
-s