Better than the unit_step definition I gave in my last email would be to
take advantage of Maxima's built-in signum function:
unit_step(x):= (signum(x)+1)/2$
Note that with this definition, unit_step(0) = 1/2.
Since signum is appropriately defined as a mathematical rather than a
computational function (simplifying rather than evaluating), Maxima
deals with it more gracefully:
plot2d( unit_step(x) ,[x,-1,1]) => works without quoting
integrate( unit_step(x)*x^2 ,x,-1,1) => works
(but Maxima doesn't handle the indefinite integral)
You might also try the absimp package, which includes simplifications
for abs and signum. It defines unitstep and unitramp.
-s