hello yongfeng,
> Thank you. I had thought that if I can use it to add a new plot to
> an existing figure. Would you like tell me whether Maxima can do it?
> i.e. if I have plot2d(sin(t),[t,0,20]); could I add another plist
> [x0,y0,x1,y1, ...,xn,yn] in it?
hmm, you can create a plot with multiple curves on it;
i think the "Plotting" documentation has some examples of that.
however, the curves must all be created by a single plot command,
i believe. so far as i know, there is no way to create one curve, then
add to it another curve.
maybe someone else has another idea.
all the best,
robert dodier