u = %pi*(-1:0.2:1)/2; 
  v = %pi/2*(-1:0.2:1);
  n = size(u,'*');
  x= cos(u)'*exp(cos(v)); /// \sleftarrow{\normalfont a surface parameterized by \verb+u+,\verb+v+}
  y= cos(u)'*sin(v);
  z= sin(u)'*ones(v);
  col=ones(u)'*cos(v); /// \sleftarrow{\normalfont a color {for} each vertex }
  col=(n-1)*(col-min(col))/(max(col)-min(col))+1; /// \sleftarrow{\normalfont rescale colors }
  drawlater(); /// \sleftarrow{\normalfont draw later ! }
  [xx,yy,zz]=nf3d(x,y,z); /// \sleftarrow{\normalfont from \verb+(x,y,z)+ to four sided faces }
  [xx,yy,zzcol]=nf3d(x,y,col); /// \sleftarrow{\normalfont change the colors as well}
  xx=[xx,-xx];yy=[yy,-yy];zz=[zz,zz];zzcol=[zzcol,zzcol]; /// \sleftarrow{\normalfont symetry}
  a=gca(); /// \sleftarrow{\normalfont handler to the current axes }
  plot3d(xx,yy,list(zz,-zzcol)); /// \sleftarrow{\normalfont Let's do it }
  f=gcf();  /// \sleftarrow{\normalfont handler to the figure }
  f3d=a.children; /// \sleftarrow{\normalfont just one child, it's our 3d plot }
  f3d.hiddencolor=n;/// \sleftarrow{\normalfont set the hidden face's colors }
  a.rotation_angles = [55,110];/// \sleftarrow{\normalfont set the view angles }
  f.color_map= graycolormap(n);/// \sleftarrow{\normalfont set the colormap \index{colormap@\texttt{colormap}}}
  drawnow(); /// \sleftarrow{\normalfont show the result on graphic window }
  xs2ps(0,'plot3d')  /// @@prerequisite 
  unix(SCI+'/bin/Blatexpr 1 1 plot3d '); /// @@prerequisite