Homework Statement
H0 = [2,0,0;0,2,0;0,0,4]
H1 = [0,1,0;1,0,1;0,1,0]
Find energy eigenvalues to 2nd order.
Homework Equations
The Attempt at a Solution
I know that I need to diagonalize the perturbation in the 2x2 subspace (for my 2 degenerate eignevalues of 2 but I'm not sure...