Discretization and domain decomposition settings when |$h = 1/2^{4}$|⁠, |$H = 1/2^{2}$| and |$\delta = h$|⁠. (a) Coarse triangulation |${\mathcal{T}}_{H}$| and fine triangulation |${\mathcal{T}}_{h}$|⁠. (b) Nonoverlapping domain decomposition |$\{ \varOmega _{k} \}_{k=1}^{N}$|⁠. (c) Overlapping domain decomposition |$\{ \varOmega _{k} ^{\prime} \}_{k=1}^{N}$|⁠.