#
# KLEIN: Test of the IF function and logical expression in the calculator
#
# Plot of a Klein bottle after Paul Bourke
#
 set camangle 55 -100 40
 set use_planes .true.
 set zoom 1

 set background &
     disc {<0,0,-1.0>,<0,0,1>,1.0 &
           pigment {checker color White color Black scale 0.15} &
           finish {Dull} }

 parametric

   map cartesian
   uname u
   vname v
   urange 0 6.283185 31  open
   vrange 0 6.283185 31  open

   c1 if( (0 <= u && u < pi) , &
          6*cos(u)*(1+sin(u))+4*(1-0.5*cos(u))*cos(u)*cos(v) , &
          6*cos(u)*(1+sin(u))+4*(1-0.5*cos(u))*cos(v+pi) )

   c2 if( (0 <= u && u < pi) , &
          16*sin(u)+4*(1-0.5*cos(u))*sin(u)* cos(v) , &
          16*sin(u) )

   c3 4*(1-0.5*cos(u))*sin(v)

   colormode none

   povray klein.pov

 endparametric

 run povray klein.pov +W400 +H400 +A0.2 +R3
 run cjpeg -Q 80 klein.tga > klein.jpg
 run rm klein.tga

 end