THE EGS5 CODE SYSTEM

the call to PEGS5 may be skipped if the working user code directory contains an existing PEGS
data file generated with parameters compatible with the current EGS5 simulation specifications.
Checks for compatibility are performed in HATCH.
B.4.3 Pre-HATCH Initializations (Step 3)
Users are strictly required to define the following variables prior to HATCH being called: NREG, the
number of regions in the geometry; MED, an array containing the material numbers (as set prior
to the call to PEGS5) of each region, and EMAXE, the maximum total energy of any electron in the
problem. No other variables used by HATCH (and then by the EGS5 system in simulating showers),
need be explicitly specified. However, if the user wishes to use any of the non-default options or
features of EGS5, the appropriate flags for invoking such requests must be specified prior to the
call to HATCH , even if the data needed to execute such options has been generated by PEGS. All
of the variables processed by HATCH in setting up an EGS5 simulation are described below.
Variables required by HATCH
EMAXE This variable, the maximum energy of an electron in the problem, is located in COMMON
USERSC found in include/egs5 usersc.f, and is used by HATCH to perform checks on the compatibility
of the EGS5 problem specification and the PEGS data file being used.
NREG HATCH uses the variable NREG when verifying and loading region-dependent options for the
problem materials.
MED The array MED, dimensioned MED(MXREG), contains the medium indices for each region (default
values are 1 for all MXREG). A medium index of zero means a region is vacuum. Indices are defined
by the order specified by the user, and are independent of the order in which the materials are
defined in the PEGS data file being used. Consider the three media example above (from the
pre-PEGS5 initialization section with vacuum defined as a fourth regions. The EGS5 user code to
accomplish this might look like:
med(1)=3
med(2)=1
med(3)=0
med(4)=2
!First region is AIR AT NTP
!Second region is LEAD
!Third region is VACUUM
!Fourth region is STEEL
Optional variables and flags processed by HATCH
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