#
#  parametric surface (star)
#
f(x,y) = 4*x*cos(y)-x*cos(4*y);
g(x,y) = 4*x*sin(y) + x*sin(4*y);
h(x,y) = -6*cos(x);

a=sur{[f(x,y),g(x,y),h(x,y)][y=0:2*pi][x=0.1:6][sample=20:40]};
plot a;
