GEOBEGIN

Summary

Starts the geometry description ​

​

See also GEOEND, PLOTGEOM
WHAT(1) > 0.0:

switches on online parenthesis expansion. If during expansion at initialization the length of an expression (measured in number of terms) exceeds the original length by a multiplicative factor NINT(WHAT(1)), expansion is aborted and online parenthesis expansion is used.

WHAT(2) > 0.0:

absolute accuracy parameter (\(A_{a}\)) in units of \(10^{-6}\) cm. It is used for tracking and boundary identification. \(A_{a}\) should be larger than \(A_{r}\times L\), where \(L\) is the largest coordinate value in the geometry description (excluding the outer black-hole shell containing it) and \(A_{r}\) is the relative accuracy achievable in double precision (of the order of \(10^{-14} \div 10^{-15}\)).

Default

= 0.0001​

WHAT(3) > 0.0:

logical unit for geometry input. The name of the corresponding file must be input on the next card if WHAT(3) is different from 5.0. Note that values of WHAT(3)≠ 5.0 and < 21.0 must be avoided because of possible conflicts with FLUKA pre-defined units.

≤ 0.0:

Set to default value of 5. Input follows.

Default

= 5.0  (i.e. geometry input follows)​

WHAT(4) > 0.0:

logical unit for geometry output​. If different from 11, the name of the corresponding file must be input on the next card if WHAT(3)= 0.0 or 5.0, otherwise on the card following the next one. Values of WHAT(4)≠ 11.0 and < 21.0 must be avoided because of possible conflicts with FLUKA pre-defined units.

≤ 0.0:

Set to default value of 11.

Default

= 11.0  (i.e. geometry output is printed on the standard output​)

WHAT(5) =

\(ip_0 + ip_1 \times 1000\), where \(ip_0\) indicates the level of parentheses optimisation and \(ip_1\), if \(>\) 0, forces the geometry optimisation even when there are no parentheses

\(ip_0\)

= 1: logical optimisation only activated

= 2: logical plus “plane” optimisation activated

= 3: logical plus “plane” plus “bounding box” optimisation activated

​

Default

:  \(ip_0 = 3\) and \(ip_1 = 0\)

WHAT(6)

: if \(>0\) it indicates the number of geometry output lines to be skipped before starting writing debugging lines. Please note that the output can rapidly become huge

SDUM

= COMBINAT: Combinatorial Geometry​ is used. See Combinatorial Geometry on Combinatorial Geometry for input description. Other geometries, available in older versions of FLUKA, are no longer supported.

SDUM

= COMBNAME: Combinatorial Geometry​ is used in free format, and names​ can be used instead of body and region numbers

.
​
SDUM

= FLUGG: The Flugg interface to the Geant4 geometry is used. In this case, the GEOEND card must immediately follow the GEOBEGIN card. The Flugg interface is available and described on the FLUKA web site.

Default

:  COMBINAT

Default

(option GEOBEGIN not given): not allowed! GEOBEGIN and GEOEND must always be present.

Notes

  1. Geometry input and output:​

    • If WHAT(3) and WHAT(4) are both ≤ 0.0, the geometry input and output are part of the standard I/O streams: the GEOBEGIN card must be immediately followed by the Combinatorial Geometry input, and then by GEOEND. (See Example 1 below).

    • If WHAT(3) is > 0.0 (and not = 5.0) and WHAT(4) is ≤ 0.0, GEOBEGIN must be followed by one card with the name of the CG input file, and then by GEOEND. (See Example 2 below).

    • If WHAT(4) is > 0.0 (and not = 11.0) and WHAT(3) is ≤ 0.0, GEOBEGIN must be followed by one card with the name of the CG output file, then by the CG input, and then by GEOEND. (See Example 3 below).

    • Otherwise, if WHAT(3) is > 0.0 (and not = 5.0), and WHAT(4) is > 0.0 (and not = 11.0), GEOBEGIN must be followed, in the order, by a line with the name of the CG input file, another line with the name of the CG output file and then the GEOEND card. (See Example 4 below).

    The first part of the CG output is essentially an echo of the input, and gives in addition some information on storage allocation of body​ and region​ data. Then follow an “Interpreted body echo”​ and an “Interpreted region echo”’​, useful in the case where free geometry input​ format has been requested. It is recommended to check on this output that the geometry description has been correctly reproduced, especially if fixed input format has been chosen, since column alignment errors are critical due to the CG strict input format. In case of severe error (“next region not found”, ​ or similar) the CG output will also contain all error and debugging messages. Minor tracking problems, however, are reported on the error message file​ (logical unit 15, see Installation and Error messages), unless reporting has been de-activated by setting WHAT(6) ≤ 0.0.

  2. Special algorithms have been implemented in the Combinatorial Geometry package of FLUKA in order to minimise tracking errors due to rounding, to improve tracking speed and to handle charged particle transport near boundaries and in magnetic fields.​

  3. A voxel geometry​ is also available in FLUKA (Voxel geometry). It is fully integrated into the FLUKA CG and it is even possible to describe a geometry partly as made of voxels​ and partly of conventional CG regions.

  4. Information on how to set up Combinatorial Geometry input is given in Combinatorial Geometry.

  5. End of geometry information must end with a GEOEND card. The same card can also be used to activate a geometry debugger.​

  6. Option PLOTGEOM allows to draw sections of the geometry on planes specified by the user. ​​

  7. Only one GEOBEGIN card is allowed.

  8. The WHAT(2) parameter might need to be increased in case of very large geometries (i.e. \(L~>~100\) m).

Example 1:

* CG Input follows, output is printed as part of Main Output
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
GEOBEGIN          0.        0.        0.        0.        0.        0.COMBINAT

Example 2:

* CG Input read from file BigHall.geo, output printed as part of Main Output
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
GEOBEGIN          0.        0.       25.        0.        0.        0.COMBINAT
BigHall.geo

Example 3:

* CG Input follows, output is printed on file geo2.out
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
GEOBEGIN          0.        0.        0.       26.        0.        0.COMBINAT
geo2.out

Example 4:

* CG Input read from file BigHall.geo, output printed on file geo2.out
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+...
GEOBEGIN          0.        0.       25.       26.        0.        0.COMBINAT
BigHall.geo
geo2.out