  The one-dimensional partially asymmetric simple exclusion process with open
boundaries is considered. The stationary state, which is known to be
constructed in a matrix product form, is studied by applying the theory of
q-orthogonal polynomials. Using a formula of the q-Hermite polynomials, the
average density profile is computed in the thermodynamic limit. The phase
diagram for the correlation length, which was conjectured in the previous
work[J. Phys. A {\bf 32} (1999) 7109], is confirmed.
