x, y, z = var("x y z") S = plot3d(x*y/(x^2+y^2), (x, -2, 2), (y, -2, 2)) show(S, aspect_ratio=1)
x, y, z = var("x y z") S = plot3d(x*y/(x^2+y^2), (x, -2, 2), (y, -2, 2), plot_points=300) show(S, aspect_ratio=1)