function sz=sigmaz(d,esta)%d es la distancia en kilometros y esta es la estabilidad ('A','B','C','D','E' o 'F')
sigz=[0.12	0.82	0.82	0.74	0.95	1
0.45	8	20	6	10	9.3
4.18019715	1.044241677	0.914461016	0.845783881	0.835685374	0.756961951
0.831176421	1.05709362	0.937871147	0.662390862	0.568212956	0.592711796
2.117622266	1.160964047	0.861353116	0.501521859	0.327358934	0.291832302
211994.7888	110.7239771	59.94926688	32.25089061	21.91973765	12
174.7769238	111.0067368	60.22842488	30.51825676	21.62106243	12
488.210833	89.4427191	75.74496322	40.7136593	37.64705882	23.47350302];
if esta=='A'
  j=1;
elseif esta=='B'
  j=2;
elseif esta=='C'
  j=3;
elseif esta=='D'
  j=4;
elseif esta=='E'
  j=5;
elseif esta=='F'
  j=6;
end
if d<sigz(1,j)
  sz=sigz(6,j)*(d^sigz(3,j));
elseif d<sigz(2,j)
  sz=sigz(7,j)*(d^sigz(4,j));
else
  sz=sigz(8,j)*(d^sigz(5,j));
end
end