The tracking medium parameters are stored in the data structure JTMED by the routine GSTMED. Details about these parameters are given in [TRAK]. They can be accessed with the routine GFTMED and printed with the routine GPTMED.
The correctness of the transport process and thus the reliability of the results obtained with GEANT depend critically on the values of the tracking medium parameters. To help the user, most of the parameters are recalculated by default by GEANT irrespective of the value assigned by the user. Advanced users can control the value of the parameters thus bypassing the automatic computation. See the description of the routine GSTMED for more information.
The tracking thresholds, and other parameters and flags that control the physics processes, defined in GINIT and possibly modified through the relevant data records, are also stored in the structure JTMED. These parameters can be redefined for each tracking medium via the routine GSTPAR.