As an example from the nuclear many-body problem, we have Schroedinger's equation as a differential equation
$$ \hat{H}\Psi(\boldsymbol{r}_1,..,\boldsymbol{r}_A,\alpha_1,..,\alpha_A)=E\Psi(\boldsymbol{r}_1,..,\boldsymbol{r}_A,\alpha_1,..,\alpha_A) $$where
$$ \boldsymbol{r}_1,..,\boldsymbol{r}_A, $$are the coordinates and
$$ \alpha_1,..,\alpha_A, $$are sets of relevant quantum numbers such as spin and isospin for a system of \( A \) nucleons (\( A=N+Z \), \( N \) being the number of neutrons and \( Z \) the number of protons).