Guys I read a little on how Heisenberg's quantum mechanics equations (solving with eigenvectors) were derived in the book "What is quantum mechanics: A physical adventure". There is no exercise in the book. After reading, I still dont understand eigenvalue. What is it for? How to use it? It seems like some kind of magical tool that can solve ALL calculation problem. Is it something like algebra, only in matrix form? Then I read this tutorial: http://algebra.math.ust.hk/eigen/01_definition/lecture2.shtml" [Broken] My reaction is: so..? Any good book/link out there that shows eigenvalue application/example? Btw, is eigenvalue under group theory or more under matrix?