function y=getLamda(fun,p1,p2)

syms lamda xn x;

dFun = diff(fun);
dFun = -2/dFun;
r1 = subs(dFun,xn,p1);
r2 = subs(dFun,xn,p2);

if(r1 > r2)
    lamda = r1;
else
    lamda = r2;
end
lamda = lamda /2;
y = lamda;