  We have calculated the effect of the inclusion of final state interactions on
pion production from nuclei with incident pion beams. We find that the effect
of absorption, along with geometric considerations, explains much of the
enhancement at low invariant mass seen in recent data for invariant mass
spectra with increasing atomic number. While the variation among nuclei is well
reproduced for all charge states, the enhancement for the ratio for heavy
nuclei to deuterium for the pi^+ pi^- final state is only partially understood.
