#### BC_SYMMETRY

###### Boundary conditions
*BC_SYMMETRY
plane, csysid${}_1$, csysid${}_2$, csysid${}_3$, $tol$
##### Parameter definition
VariableDescription
plane Symmetry planes through the origin
options: X, Y, Z, XY, YZ, ZX, XYZ
csysid${}_1$ ID of coordinate system defining location and orientation (optional) of first symmetry plane. This input is only active if plane=0.
csysid${}_2$ ID of coordinate system defining location and orientation (optional) of second symmetry plane. This input is only active if plane=0.
csysid${}_3$ ID of coordinate system defining location and orientation (optional) of third symmetry plane. This input is only active if plane=0.
$tol$ maximum distance between a node and the symmetry plane for symmetry conditions to be applied
##### Description

This command defines up to three symmetry planes at $x$, $y$ or $z=0$ or at the origin of specified coordinate systems. When referring to a local coordinate system, the symmetry plane normal is defined as the local x-direction of the coordinate system. The normal direction of the nearest element face is taken as symmetry plane normal in case the local x-direction has not been explicitly defined in the coordinate system command.

Appropriate boundary conditions are automatical applied to nodes located on a symmetry plane. External faces on a symmetry plane are excluded from the contact.

Symmetry conditions are also applied to the boundary of the global particle domain (see PARTICLE_DOMAIN).

Symmetry planes can also be used as rigid frictionless walls, that nodes can not penetrate.

##### Example
###### Symmetry plane

The following commands apply symmetry boundary conditions on a surface. A point on the symmetry plane is defined through a local coordinate system with ID = 20. The normal of the nearest element face is used as symmetry plane normal.

*PARAMETER
x0 = 0.2
y0 = 0.0
z0 = 0.1
*BC_SYMMETRY
0, 20
*COORDINATE_SYSTEM_FIXED
20, [%x0], [%y0], [%z0]