GEOM410 Ordering the contents of a volume

In the case of a mother volume containing a large number of daughters, tracking can be rather slow. This is due to the fact that each time GEANT requires to know in which daughter it is or will be tracking, it search through the whole list of daughter volumes. This is done by GEANT creating for every daughter volume a list which contain pointers to all the daughters of the same mother.

Clearly this may be avoided, because at any step of tracking, the coordinates and direction cosines of the current step are known. From this and the knowledge of the geometry, a restricted list of daughter volumes to be searched can be built. This can be accomplished in GEANT in two ways, which are described in this chapter.

Note: the user must be aware that the following routines alter the default search list of daughters of a given mother. A user mistake can cause wrong transport because GEANT does not make any check on the correctness of the list of neighbours provided by the user.

• Static ordering
• Dynamic ordering