doc/info/figures/plotting21.mac

   1 expr_1: 5*cos(x)*(cos(x/2)*cos(y)+sin(x/2)*sin(2*y)+3)-10$
   2 expr_2: -5*sin(x)*(cos(x/2)*cos(y)+sin(x/2)*sin(2*y)+3)$
   3 expr_3: 5*(-sin(x/2)*cos(y)+cos(x/2)*sin(2*y))$
   4 plot3d ([expr_1,expr_2,expr_3], [x,-%pi,%pi], [y,-%pi,%pi], [grid,50,50],
   5   [pdf_file,"./plotting21.pdf"]);
   6 plot3d ([expr_1,expr_2,expr_3], [x,-%pi,%pi], [y,-%pi,%pi], [grid,50,50],
   7   [png_file,"./plotting21.png"]);