// --------------------------------------- parametric surface -------------- 
parametric{
  function{ sin(u)+0.25*sin(v*2*pi)}// x(u,v)
  function{ cos(u) }   // y(u,v)
  function{ v }        // z(u,v)
  <0,-2>,<2*pi,2>  // start, end (u,v)
  contained_by {box {<-2,-2,-2>,<2,2,2>}}
  max_gradient 7
  accuracy 0.005
  precompute 18 x,y,z
  texture{
    pigment{ color rgb<1,1,1>*.8}
    finish { phong 0.1 }}
  scale 0.5
} // end of parametric -----------------------------------------------------