MATLAB: Arrêter l’itération à une certaine valeur

HI!
I have a vector length of 0:0.1:1 and ineed iteration according to this vector length. I have done this part now i need to stop these iteration when valuee of r becomes positive but it doesnt work what should i do.Hve a look on this code.I need the loop to break when real part of poles that is r (any of three values in vectoor) becomes +ive but it doesn;t work.The condition work perfectly for r<0 condition but not for this.plzz help
 

for k= 0:0.1:1
n=conv(k,[0.5 1.3]);
d=[1 1.2 1.6 0];
sys1=tf(num1,den);
P=pole(F);
r=real(P)
if r>0
break
end
end