  To develop a unitary quantum theory with probabilistic description for
pseudo- Hermitian systems one needs to consider the theories in a different
Hilbert space endowed with a positive definite metric operator. There are
different approaches to find such metric operators. We compare the different
approaches of calculating pos- itive definite metric operators in
pseudo-Hermitian theories with the help of several explicit examples in
non-relativistic as well as in relativistic situations. Exceptional points and
spontaneous symmetry breaking are also discussed in these models.
