sets the minimum and maximum step size on a region-by-region basis for
transport of all charged particles (hadrons, muons and electrons)
(see also EMFFIX, FLUKAFIX, MULSOPT, MGNFIELD)
WHAT(1) >= 0.0 : minimum step size in cm (overrides, if larger, region
by region the overall minimum step implicitly set by
WHAT(2) of MGNFIELD)
< 0.0 : whatever happens, the location of boundary intersection
will be found with an uncertainty =< |WHAT(1)|. Of
course, for a given boundary, this value should be
applied to both regions defining the boundary.
Default: no default
WHAT(2) = maximum step size in cm
Default = 100000. cm for a region without magnetic field
= 10. cm for a region with magnetic field
= twice the minimum step if the latter has been
defined larger than the maximum (Not implemented
yet)
WHAT(3) = lower bound of the region indices in which the indicated
step size is to be applied ("From region WHAT(3)...").
Default: = 2.0
WHAT(4) = upper bound of the region indices in which the indicated
step size is to be applied ("...to region WHAT(4)...")
Default: = WHAT(3)WHAT(5) = step length in assigning indices. ("...in steps of
WHAT(5)").
Default: 1.0
WHAT(6), SDUM : not used
Default (option STEPSIZE not given): the above defaults apply in
all regions (10 cm with magnetic field, 1.E5 cm without)
Note: this option differs from EMFFIX and FLUKAFIX for the following
main reasons:
. it is given by region rather than by material
. therefore, it is effective also in vacuum regions
. the maximum step is determined in an absolute way (i.e., in cm)
rather than in terms of maximum energy loss
. it allows to set not only a maximum but also a minimum
step length. This may be necessary in order to avoid the forcing
of extremely small steps when a low-energy charged particle
spirals in a magnetic field. Option MGNFIELD offers a similar
possibility, but not tuned by region.
Option STEPSIZE may be essential in and around regions of very
small dimensions or in regions where a magnetic field is present
(and is rarely required otherwise).
The maximum step size for a given region can be decided from
the following considerations:
- in a region with magnetic field it should not be larger than
the minimum dimension of the region itself and of its
neighbor regions. Obviously, it should also be larger than
the minimum step possibly imposed by MGNFIELD or by STEPSIZE
itself.
- in a non-vacuum region, it should not be larger than about
one-third of its minimum dimension, in order to allow
the multiple-scattering algorithm to work in optimal
conditions.
Example:
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
ASSIGNMAT 2.0 15.0 30.0 5.0 1.0 0.0
* A magnetic field is present in vacuum regions 15, 20, 25 and 30.
MGNFIELD 20.0 0.2 0.10 0.0 0.0 0.0
STEPSIZE -0.05 0.0 20.0 25.0 0.0 0.0
STEPSIZE 0.3 0.0 15.0 0.0 0.0 0.0
* The maximum deviation angle due to magnetic field in any step is set
* = 20 degrees, and boundary crossings must be identified with an error
* not larger than 2 mm. If the max. angle constraint forces the step to
* be shorter than 10 cm, the step will be set = 10 cm in region 20, 25, 30,
* but will be set = 3 mm in region 15 (WHAT(1) of STEPSIZE overrides the
* general setting due to WHAT(3) of MGNFIELD). Whatever the size of the
* step, however, the accuracy of the boundary crossing position must be
* equal or better than 0.5 mm in regions 20 and 25 (probably contiguous,
* since the same accuracy must be set for regions on either side of a
* boundary). The value of the magnetic field will be provided at each
* step by the user routine MAGFLD.
