plot3d (r^.33*cos(th/3), [r,0,1], [th,0,6*%pi], nobox, nolegend,
   [grid, 12, 80], [transform_xy, polar_to_xy], [pdf_file,"./plotting23.pdf"]);
plot3d (r^.33*cos(th/3), [r,0,1], [th,0,6*%pi], nobox, nolegend,
   [grid, 12, 80], [transform_xy, polar_to_xy], [png_file,"./plotting23.png"]);
