Voxel and tetrahedron geometry options
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.. list-table:: **icells**
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   * - Value
     - Explanation
   * -  | (D=3)
     -  | Read and write [cell] section in binary.  The concept is similar to ivoxel parameter, but the entire [cell]  section is turned into binary files.  However, if your geometry contains a numerous number of cells with simple  definitions, the computational time may increase by using this option.  Furthermore, this function cannot be used when different densities are  defined for a given material number.
   * -  | =0
     -  | Not using file(19).  No input echo for [cell] section.
   * -  | =1
     -  | Read [cell] section from binary files named file(19) and  file(19).cfg.  No input echo for [cell] section.  ivoxel is automatically set to 1.
   * -  | =2
     -  | Write down [cell] section in binary files named file(19) and  file(19).cfg.  No input echo for [cell] section.  ivoxel is automatically set to 2.
   * -  | =3
     -  | Not using file(19) (conventional mode).  Output input echo for [cell] section.
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.. list-table:: **ivoxel**
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   * - Value
     - Explanation
   * -  | (D=0)
     -  | Read and write voxel data in binary.
   * -  | =0
     -  | Not using file(18).
   * -  | =1
     -  | Read from voxel data in binary file(18).
   * -  | =2
     -  | Write down voxel data in binary on file(18).
   * -  | =3
     -  | Same action as =0 but voxel data echo is included in input echo  (no voxel data echo for other options).

The ivoxel parameter can be used to accelerate calcutions with voxel geometry.  When performing PHITS calculation with ivoxel=2, voxel data are  output in file(18) in binary format, and the calculation is then stopped (until  ver. 2.30, calculation was continued).  In the next calculation with ivoxel=1, the necessary information is read  from file(18) created in the previous calculation with ivoxel=2,  so the data output process is omitted and the calculation time is shortened.  Note that this parameter is not available in the case that the  description after fill includes universe numbers with the  transformation of the coordinate system, e.g., 3(1 0 1). 

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.. list-table:: **itetvol**
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   * - Value
     - Explanation
   * -  | (D=0)
     -  | Options to compute volume of tetrahedron geometry for LAT=3.
   * -  | =0
     -  | The volume will not be computed.
   * -  | =1
     -  | The volume will be automatically computed and used in tallies, etc.
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.. list-table:: **itetra**
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   * - Value
     - Explanation
   * -  | (D=0)
     -  | Read and write tetrahedron geometry data in binary.  Binary file must be re-constructed by setting itetra=2 when  ntetsurf and/or ntetelem are changed.
   * -  | =0
     -  | Not using the data file.
   * -  | =1
     -  | Read from tetrahedron geometry data in binary file(30)(D=Tetra.bin).
   * -  | =2
     -  | Write down tetrahedron geometry data in binary file(30)(D=Tetra.bin).
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.. list-table:: **ntetsurf**
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   * - Value
     - Explanation
   * -  | (D=100)
     -  | Number of outer surfaces of tetrahedron geometry allowed for each  sub-space of the container box.
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.. list-table:: **ntetelem**
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   * - Value
     - Explanation
   * -  | (D=200)
     -  | Number of elements of tetrahedron geometry allowed for each sub-space  of the container box.
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.. list-table:: **itetauto**
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   * - Value
     - Explanation
   * -  | (D=0)
     -  | Options to automatically create cells corresponding to universes of  tetrahedron geometry.
   * -  | =0
     -  | No cell is automatically created.
   * -  | =1
     -  | The cells will be automatically created. The text file (.txt) is required for the TetGen format.
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.. list-table:: **itgchk**
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   * - Value
     - Explanation
   * -  | (D=0)
     -  | Option to check irregular zero-volume tetrahedrons and intersections among tetrahedrons in  tetrahedron geometries.
   * -  | =0
     -  | No check.
   * -  | =1
     -  | The irregular geometry check will be performed and the program ends  abruptly without further computation [#]_ . Choose 0 for transport calculation etc.  The first detected irregular geometry will be outputted into the  "tet\_geoerr.inp" file.  The situation can be checked with this file by PHIG3D.

Using the option of itetvol=1, when the tetrahedron geometry is treated  with LAT=3, the volume of the universes appearing in tetrahedron geometry  can be automatically computed.  However, the volume is computed by simply summing up the volumes of  individual tetrahedrons, which might produce incorrect values in cases  in which tetrahedron geometry is clipped out through the use of nest structure  of "universe"and "fill".  The computed value with the option of itetvol=1 is given priority over values specified in the [volume] or other sections. 

When tetrahedron geometry (LAT=3) is used in PHITS calculation,  necessary information for transport calculation is generated by reading  the tetrahedron geometry file prior to the actual transport calculation.  This process becomes computationally heavy as the number of elements  in the tetrahedron geometry increases.  In such case, the itetra parameter can be used to reduce the  computational time.  Performing PHITS calculation with itetra=2 will have the processed  tetrahedron geometry data recorded in the binary file  file(30)(D=Tetra.bin) followed by the calculation being stopped.  In the next calculation with itetra=1, the necessary information  is read from the Tetra.bin file, and the data generation process is  omitted to reduce the calculation time. 

The ntetsurf and ntetelem parameters are associated with the  two algorithms sub-dividing the box containing the tetrahedron geometry  for PHITS calculations with (LAT=3), which reduce the computational time  by limiting the number of elements belonging to each sub-space. One algorithm finds a surface of the tetrahedron geometry when a  particle enters the geometry.  The container box is sub-divided so that the number of outer surfaces at  each sub-space is less than ntetsurf.  The other algorithm finds an element of tetrahedron geometry when a  particle is initiated inside the geometry.  The box containing all tetrahedron elements is subdivided so that the  number of elements belonging to each sub-space is less than  ntetelem. 

Using the option of itetauto=1, cells required by each tetrahedron with specfied universe in tetrahedron geometry are created automatically. The cost manually creating the cells can be reduced with this option when the number of universes contained in tetrahedron geometry increase. This option is especially helpful when the tetrahedron geometry is imported with the NASTRAN bulk data format. See the explanation of tetrahedron geometry in **[cell]** for more details.

.. [#]  Instead of 1, by specifying number  :math:`n<11` , the geometry of the  :math:`n` -th  detected error will be outputted into the  "tet\_geoerr.inp" file.  The check will end after finding 10 irregular intersections so no file  will be created when a number more than 10 is specified.