// --------------------------------------- parametric surface -------------- 
parametric{ 
  function{ u*v*sin(15*v) }
  function{ v }   
  function{ u*v*cos(15*v) }
  <0,-1>,<1,1>
  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>}
            finish {  phong 0.5  }
	  }
  scale <0.5,0.5,0.5>
  rotate <0, 0, 0>
  translate < 0, 0.5, 0>
} // end of parametric -----------------------------------------------------