axis([0 20 -2 1])
x=0:0.01:20;
for k = 0:2
    y= bessely(k,x);
    hold on;   
    if k == 0
        plot(x,y,'k');
    end
    if k == 1
        plot(x,y,'k:');
    end
    if k == 2
        plot(x,y,'k--');
    end
end
