Added back Predictor-Corrector solution of KBequations. NOT WORKING!
We have a problem here.
The solution from this code is different from the same solution with working predictor-corrector
code from nomix_devel branch.
The 2d-interpolation of the Self-energy is giving many problems.
I am losing my optimism... :(
For the time being I won't debug the alternative PreCorr routine, focuing on the
Runge-Kutta one. I need to understand how much the sigma function is creating problems.
It may also be the NEQ_IPT. check it out.