Introduction.

EXAMPLES:

sage: x, y = var('x y')
sage: W = plot3d(sin(pi*((x)^2+(y)^2))/2,(x,-1,1),(y,-1,1), frame=False, color='purple', opacity=0.8) 
sage: S = sphere((0,0,0),size=0.3, color='red', aspect_ratio=[1,1,1])
sage: show(W + S, figsize=8)