# channelflow.org

### Site Tools

docs:utils:symmetryop

# symmetryop

symmetryop: apply a symmetry operation to a given field

options :
-sn       --sn       <int>       default == 0     apply s1, s2, or s3 symmetry (0 => use sx,sy,sz,ax,az,a)
-sx       --x-sign                                change u,x sign
-sy       --y-sign                                change v,y sign
-sz       --z-sign                                change w,z sign
-ax       --axshift  <real>      default == 0     translate x by ax*Lx
-az       --azshift  <real>      default == 0     translate z by az*Lz
-anti     --anti                                  antisymmetry instead of symmetry
-v        --verbose                               print out some diagnostics
<flowfield>  (trailing arg 2)                     input field
<flowfield>  (trailing arg 1)                     output field

The symmetries of 3D fields on x,z periodic, y bounded domains with Dirichlet or Neumann conditions at the walls can be parameterized as

where s,sx,sy,sz, and are +/-1 and ax,az are real. The options to symmetryop set the values of these parameters, and the resulting symmetry is applied to the input field and saved to disk as the output field. The -sx,-sy,-sz options work as flags: using -sx sets sx = -1; otherwise sx = 1. Likewise the -anti option sets s = -1.

For convenience the -sn option allows application of a few predefined symmetries that figure prominently in our research, namely

# Usage examples

## Translation

Translate the field g.ff by Lx/2 in x and save it in h.ff

  symmetryop -ax 0.5 g h

## General

Apply s1 = [u,v,w] -> [-u, -v, w](-x + L_x/2 , -y, z+L_z/2) to g.ff and save it in h.ff

  symmetryop -sx -sy -ax 0.5 -az 0.5 g h

## Convenience

Apply s1 to g.ff and save it in h.ff, using the convenience -sn option

  symmetryop -sn 1  g h