Editing Input syntax manual (section)

=== set usym ===

 '''set usym''' ''UNI AX BC X<sub>0</sub> Y<sub>0</sub> &theta;<sub>0</sub> &theta;<sub>w</sub>'' [ ''OPT'' ] 

Defines a universe symmetry. Input values:

{|
| <tt>''UNI''</tt> 
| : universe name
|-
| <tt>''AX''</tt> 
| : symmetry axis (x-axis = 1, "<tt>x</tt>", y-axis = 2, "<tt>y</tt>", z-axis = 3, "<tt>z</tt>")
|-
| <tt>''BC''</tt> 
| : boundary condition (reflective = 2, "<tt>reflective</tt>", periodic = 3, "<tt>periodic</tt>")
|-
| <tt>''X<sub>0</sub>''</tt> 
| : x-coordinate of the origin [in cm]
|-
| <tt>''Y<sub>0</sub>''</tt> 
| : y-coordinate of the origin [in cm]
|-
| <tt>''&theta;<sub>0</sub>''</tt> 
| : azimuthal position where the symmetry segment starts [in degrees]
|-
| <tt>''&theta;<sub>w</sub>''</tt> 
| : width of the segment [in degrees]
|-
| <tt>''OPT''</tt> 
| : option to use actual reflections and translations (1/yes) instead of coordinate transformations (0/no). (default value: 0)
|}

<u>Notes:</u>
*Usage:
**To simplify construction of complex geometries.
**To reduce the number of burnable material zones when [[automated depletion zone division]] is applied (see [[#div|div]] card).
*Symmetry application:
**Using coordinate transformations.
***Symmetry not allowed on root universe with repeated boundary conditions (see [[#set bc|set bc]] option).
***The particle position and direction are not affected during tracking.
**Using actual reflections and translations.
***Symmetry only allowed on root universe
***The results of surface current and flux detectors ('''ds''' entry in [[#det|det]] card) or produced, e.g., by the [[#set adf|set adf]] or  [[#set alb|set alb]] options might not be correct.
***Track plots (launched with the [[Installing and running Serpent#Running Serpent|<tt>''-tracks''</tt>]] command line option) do not work properly.
*Remember:
**With lattices, to prevent excess memory usage during depletion, the lattice positions overlapped by the symmetry should remain empty of fuel pins, for example.
**It is important to pay attention to the [[Defining material volumes|definition of material volumes]].
**The supported Serpent 1 syntax-style: '''set usym''' <tt>''UNI''</tt> <tt>''SYM''</tt> [ <tt>''X<sub>0</sub>''</tt> <tt>''Y<sub>0</sub>''</tt> ] allows only quadrant symmetries (<tt>''SYM''</tt> = 4) in universe 0 (<tt>''UNI''</tt> = 0) centred in origin (<tt>''X<sub>0</sub>''</tt>, <tt>''Y<sub>0</sub>''</tt>) = (0,0).
*For more information, see examples on [[universe symmetries]].