Fix bug in offset.

21_distributed-memory.tex

@@ -433,7 +433,7 @@ For further uniform refinement, this mesh size must be scaled by a factor $3^{-i
 
 Another family of interesting uniform meshes are the ones with $3^i \times 48^d$ cells that are shifted
 by $3^i \times 3$ cells. They can be created by choosing $\texttt{ranks\_per\_dimension}=16$
-and $\texttt{outside\_cells\_left}=3$. The latter must be multiplied by a factor $3^i$ for any
+and $\texttt{outside\_cells\_left}=1$. The latter must be multiplied by a factor $3^i$ for any
 additional refinement level to preserve the positioning.
 The $48^d$ mesh requires a maximum-mesh-size of $\frac{1}{48} \approx 0.021$.
 For further uniform refinement, the mesh size must be scaled with a factor $3^{-i}$.