function pfeilportrait(y,format,pos,gr,br)

plot(y(:,1),y(:,2),format);

hold on;

d = ceil(length(y).*pos);

for i=1:length(pos);
    j=d(i);
    dy = y(j,:)-y(j-1,:);
    if (gr<0)
        dy = -gr*dy;
    else
        dy = gr*dy./norm(dy,2);
    end;
    arrow(y(j-1,:),y(j,:));
    %a1 = [cos( br) sin( br); -sin( br) cos( br)] * dy';
    %a2 = [cos(-br) sin(-br); -sin(-br) cos(-br)] * dy';
    %plot([y(j,1) y(j,1)-a1(1)], [y(j,2) y(j,2)-a1(2)], format);
    %plot([y(j,1) y(j,1)-a2(1)], [y(j,2) y(j,2)-a2(2)], format);
end