Construct the functional \(S [ \psi , \psi ^ { \dagger } ]\) whose variation with respect to \(\psi = \psi ( \vec { r } , t )\) and \(\psi ^ { \dagger } = \psi ^ { \dagger } ( \vec { r } , t )\) gives
the Schrodinger equation \(i \hbar \frac { \partial \psi } { \partial t } = \hat { H } \psi\) and its conjugated,
the stationary Schrodinger equation \({ \hat { H } } \psi = E \psi\) and its conjugated.
Here \(\hat { H }\) is some hermitian operator.