x=[-10:1:10];
n=size(x,2);
y=zeros(n,1);
for i=2:2:n
  y(i)=2/(pi*x(i));
end;
for i=1:2:n
  y(i)=0;
end;
plot(x,y,'o','MarkerEdgeColor','k','MarkerFaceColor','k','MarkerSize',2);
axis([-10 10 -0.8 0.8]);
axis on;
