Some Surfaces

sombrero

> plot3d(sin(sqrt(x^2+y^2))/sqrt(x^2+y^2),x=-10..10,y=-10..10);

> plot(sin(sqrt(x^2))/sqrt(x^2),x=-10..10);

monkey saddle

> plot3d(x*(x^2-y^2),x=-3..3,y=-3..3,orientation=[50,75]);

dog saddle

> plot3d(x*y*y*(x^2-y^2),x=-3..3,y=-3..3,orientation=[50,75]);