Gp = tf(0.4,[2.4 10.24 11 1]);
[y,t] = step(Gp);
ypp = diff(y,2);
t_infl = fzero(@(T) interp1(t(2:end-1),ypp,T,'linear','extrap'),0);
y_infl = interp1(t,y,t_infl,'linear');

plot(t,y)
%axis([0 60 -1 1.5 ])
grid
hold on
plot(t_infl,y_infl,'ro')
A = [1.0597,1.2716];
B = [0.0899,0.1168];
plot(A,B,'*')

xlim = get(gca,'XLim');
m = (B(2)-B(1))/(A(2)-A(1));
n = B(1)*m-0.0560;
y1 = m*xlim(1) + n;
y2 = m*xlim(2) + n;
line([xlim(1) xlim(2)],[y1 y2],'color','red')
hold off