import graph_pi;

graphicrules(xunit=1cm, yunit=3cm,
             xmin=-2pi, xmax=2pi, ymin=-1, ymax=1);

grid(xStep=pi/2, xstep=pi/4, yStep=.5, ystep=.25);

cartesianaxis(xticks=Ticks(Label(Fill(white)),
                           labelfrac(factor=pi,symbol="\pi",symbolin=true,
                                     zero=false),Step=pi/2, step=pi/4, ptick=grey),
              yticks=Ticks(Label(Fill(white)),
                           labelfrac(zero=false),Step=.5,step=.25, ptick=grey), Arrow);

dot("$O$",(0,0),2SW);

shipout(bbox(Fill(white)));