The material property GROUPVEL (group velocity) is automatically calculated from material property RINDEX (refractive index), when RINDEX is defined. However adding an entry to RINDEX with MPT->AddEntry(“RINDEX”, e[ie],RINDEX); does not trigger a recalculation of GROUPVEL. Thanks to Bernardo Tomé for reporting. Discourse discussion: https://geant4-forum.web.cern.ch/t/optical-photon-velocity/4035/3
This is now fixed. This functionality is now used in the OpNovice example.