function polygon(X,str)

axis([min(X(1,:))-3 max(X(1,:))+3 min(X(2,:))-3 max(X(2,:))+3]);
hold on
plot([X(1,:)./X(3,:) X(1,1)./X(3,1)],[X(2,:)./X(3,:) X(2,1)./X(3,1)],str);
hold off