How to get dynamic response using unitary eigenvectors as initial conditions to excite modes

Dear all,

I found in the book, Adances in uUnmanned Aerial Vehicles State of the Art and the Road to Autonomy

In page 130, chapter 5.4.1, it said that unitary eigenvectors are used as initial conditions to excite modes and obtain dynamic response, did it mean as following:

for linear state space eqaution dotx = A * x + B * u, we could get its eigenvalues and eigenvectors using function eig(A), but how to get unitary eigenvectors?

How to using unitary eigenvectors as input to excite modes? I used function initial() but it did not work! Thanks