Killan's VAR stationarity adjustment
shrink_Phi(Phi_tilde, Phi_hat, ev_restr)
stationary VAR(1)
VAR (1) bias-corrected feedback matrix from Bauer, Rudebusch and, Wu (2012)
unrestricted VAR(1) feedback matrix
maximum eigenvalue desired in the feedback matrix after the adjustement
Bauer, Rudebusch and, Wu (2012). "Correcting Estimation Bias in Dynamic Term Structure Models".
This function is an adapted version of the"shrink_Phi" Matlab function available at Cynthia Wu's website
(https://sites.google.com/view/jingcynthiawu/).