Automatic calculation of parameters

The definition of a tracking medium requires the specification by the user of a set of parameters (see [CONS200]) which can critically affect the tracking and hence the physics results of the GEANT MonteCarlo. To help the user to find the optimal set of parameters, by default GEANT overrides the values of STMIN, DEEMAX, STEMAX and TMAXFD. This behaviour is controlled by the AUTO data record and interactive command. By default AUTO=1 and automatic evaluation of the parameters is enforced (see below for the partly anomalous behaviour of TMAXFD). When AUTO=0 then only those parameters which are < 0 are recalculated by GEANT, while for the others the user input is accepted with minimal checking.

When the automatic calculation of parameters is active, the following applies:

DEEMAX

The formula used by GEANT is the following:

$0.25$	$if$	$ISVOL=0$	$and$	$X$0<2 &sp;cm
$0.25-\{0.2X$0}	$if$	$ISVOL=0$	$and$	$X$0≥2 &sp;cm
$\{0.2X$0}	$if$	$ISVOL\ne 0$
$$

$.$

$ISVOL>\; 0$ defines a sensitive detector, while $ISVOL\le 0$ is a non- sensitive detector (see [HITS]).

STMIN

The default value corresponds to a stopping range of 200 keV above CUTELE.

TMAXFD

The default value corresponds to $20○$ if the input value to GSTMED is $\le 0$ or $>\; 20○$ , otherwise the input value is taken.

STEMAX

The default value is $1010$ ( BIG variable in common /GCONST/).

These values have been tuned empirically on a variety of setups and users are invited to start with automatic computation. The values of the parameters can be checked with a call to GPRINT('TMED',0) after GPHYSI has been called. Use of AUTO mode is strongly recommended because it makes GEANT a predictive tool. In this way all parameters are automatically computed by the system as opposed to tuning data and MonteCarlo via the tracking parameters.