% --- start of displayed preamble in the book --- input featpost3Dplus2D % --- end of displayed preamble in the book --- % graphic converted to gray in book using 'color2gray' defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) def zsurface( expr xc, yc ) = cosd(xc*57)*cosd(yc*57) +4*mexp(-(xc**2+yc**2)*6.4) enddef; f := 7*(4,1,5); Spread := 35; LightSource := 10*(4,-3,4); SubColor := 0.4background; numeric np, ssize; path chair; np = 20; ssize = 5; hexagonaltrimesh( true,np,ssize,zsurface); endfig; end;