simplest case the eigenvalue {\displaystyle \lambda }\lambda is non-degenerate and the probability is given by {\displaystyle |\langle {\vec {\lambda }},\psi \rangle |^{2}}{\displaystyle |\langle {\vec {\lambda }},\psi \rangle |^{2}}, where {\displaystyle {\vec {\lambda }}}{\displaystyle {\vec {\lambda }}} is its associated eigenvector.