// --------------------------------------- parametric surface -------------- 
parametric{
  function{ u }     //x(u,v)
  function{ 0.5*v*sin(u*2*pi)} //y(u,v)
  function{ v }     //z(u,v)
  <-4,-2>,<4,2> // start, end (u,v)
  contained_by {box {<-1,-1,-1>,<1,1,1>}}
  max_gradient 5
  accuracy 0.0035
  precompute 18 x,y,z
  texture {
    pigment{ color rgb<1,1,1>*1.2}
    finish { phong 0.5 } }
  scale  0.5
} // end of parametric -----------------------------------------------------