% --- start of displayed preamble in the book --- % --- end of displayed preamble in the book --- defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) def f(expr a)=sind(a) enddef; numeric u; u=5mm; path p; numeric n; n=16; p=(0,f(0)) for i:=1 upto n: .. ((i/n)*10u,3u*f(i*(360/n))) endfor; draw p; endfig; end;