  Analytic and numeric approximations are studied in detail for a hydrodynamic
parameterization of single-particle spectra and two-particle correlation
functions in high energy hadron-proton and heavy ion reactions. Two very
different sets of model parameters are shown to result in similarly shaped
correlation functions and single particle spectra in a rather large region of
the momentum space. However, the absolute normalization of the single-particle
spectra is found to be highly sensitive to the choice of the model parameters.
For data fitting the analytic formulas are re-phrased in terms of parameters of
direct physical meaning, like mean transverse flow. The difference between the
analytic and numeric approximations are determined as an analytic function of
source parameters.
