& w & r & b & r
\end{pmatrix}.$$ As a result, the initial pattern $F$ is given by the substitution $\sigma$ applied to $F = (f~f~f)$, that is $$\sigma(F) = \bigl(\sigma(f) ~ \sigma(f) ~ \sigma(f)\bigr) =
\begin{pmatrix}
  b & w & b & w & b & w \\
  r & w & r & w & r & w \\
  b & r & b & r & b & r \\
  r & b & r & b & r & b \\
  w & r & w & r & w & r \\
  w & b & w & b & w & b \\
  w & r & w & r & w & r \\
  r & b & r & b & r & b \\
  b & r & b & r & b & r \\
  r & w & r & w & r & w
\end{pmatrix}.$$

For the larger domain $\Omega = [-30, 30]\times [-20, 20]$, the associated standing wave pattern $B(x,y)$ is reported in Figure \[fig:f3\]. An elementary $32\times 22$ discrete pattern of blue ($b$), red ($r$) and white ($w$) spots is identified and delimited by a 