Editing Input syntax manual (section)

=== set bc ===

 '''set bc''' ''MODE''

 '''set bc''' ''MODE ALB''

 '''set bc''' ''MODEX MODEY MODEZ''

 '''set bc''' ''MODEX MODEY MODEZ ALB''
Sets the boundary conditions (BCs). Input values:

{|
| <tt>''MODE''</tt>
| : boundary condition type in all directions
|-
| <tt>''MODEX''</tt> 
| : boundary condition type in x-direction 
|-
| <tt>''MODEY''</tt> 
| : boundary condition type in y-direction 
|-
| <tt>''MODEZ''</tt> 
| : boundary condition type in z-direction
|-
| <tt>''ALB''</tt> 
| : albedo
|}

The possible boundary condition types are:
::{| class="wikitable" style="text-align: left;"
! Type
! Description
! Notes
|-
| <tt>1, black</tt>
| vacuum boundary condition(s)
| the particle is killed
|-
| <tt>2, reflective</tt>
| repeated (reflective) boundary condition(s) 
| the particle is reflected back into the geometry
|-
| <tt>3, periodic</tt>
| repeated (periodic) boundary condition(s)
| the particle is moved to the opposite side of the geometry
|-
|}

<u>Notes:</u>
*The default boundary condition is vacuum in all directions.
*Direction-wise boundary conditions:
**Boundary conditions can be set for all directions at once: <tt>''MODE''</tt>.
**Boundary conditions can be set for x-/y-/z- direction separately: <tt>''MODEX''</tt>, <tt>''MODEY''</tt>, and <tt>''MODEZ''</tt>
*Boundary conditions can be defined with albedos by adding one additional parameter in the list, <tt>''ALB''</tt>.
**Albedo boundary conditions are invoked by multiplying the particle weight with factor <tt>''ALB''</tt> each time a reflective or periodic boundary is hit.
*Repeated boundary conditions (reflective or periodic):
**They are based on universe transformations, which limits outer boundary to surfaces that form regular lattices (square and hexagonal prisms, rectangles, cubes and cuboids).
**They are applied on the first surface of outside cells (see definition of outside cells in the [[#cell|cell card]])
*For universe symmetry options, see the [[#set usym|set usym]] option.
*For more information, see the detailed description on the [[Boundary conditions|Boundary conditions]].