A = diag([-4 -2 -2 -2 -1 -1]) + diag([3 2 1 1 1],1) + diag([ones(5,1)],-1)

b = [9.6 -3.7 1.1 -1.2 2.0 -1.9]';

pertub = 0.05;
b1 = b + pertub * [-1 1 -1 1 -1 1]';
b2 = b + pertub * [1 1 1 -1 -1 -1]';
b3 = b + pertub * [1 1 -1 -1 1 1]';

x = A\b;
x1 = A\b1;
x2 = A\b2;
x3 = A\b3;

xnorm_inf = norm(x,inf)
bnorm_inf = norm(b,inf)

EMF1 = (norm(x-x1,inf)/xnorm_inf)/(norm(b-b1,inf)/bnorm_inf)
EMF2 = (norm(x-x2,inf)/xnorm_inf)/(norm(b-b2,inf)/bnorm_inf)
EMF3 = (norm(x-x3,inf)/xnorm_inf)/(norm(b-b3,inf)/bnorm_inf)

cond_est = max([EMF1,EMF2,EMF3])
norm(A,inf)*norm(inv(A),inf)


disp([x x1 x2 x3])

