Figure 5

Relative boundary error ${\mathit{e}}_{\mathit{N}}$ as a function of the order N of the truncated Fourier-like series expansion representing the solution of the Dirichlet problem for the Laplace equation in the supershaped annulus $\mathcal{A}$ described by the Gielis formula with parameters ${\mathit{k}}_{\mathit{x}}^{\mathbf{-}}\mathbf{=}{\mathit{k}}_{\mathit{y}}^{\mathbf{-}}\mathbf{=}\mathbf{2}$ , ${\mathit{d}}_{\mathit{x}}^{\mathbf{-}}\mathbf{=}\mathbf{1}\mathbf{/}\mathbf{2}$ , ${\mathit{d}}_{\mathit{y}}^{\mathbf{-}}\mathbf{=}\mathbf{1}$ , ${\mathit{\nu }}_{\mathit{x}}^{\mathbf{-}}\mathbf{=}\mathbf{2}$ , ${\mathit{\nu }}_{\mathit{y}}^{\mathbf{-}}\mathbf{=}{\mathit{\nu }}_{\mathbf{0}}^{\mathbf{-}}\mathbf{=}\mathbf{4}$ , ${\mathit{k}}_{\mathit{x}}^{\mathbf{+}}\mathbf{=}{\mathit{k}}_{\mathit{y}}^{\mathbf{+}}\mathbf{=}{\mathit{k}}^{\mathbf{+}}\mathbf{=}\mathbf{4}$ , ${\mathit{d}}_{\mathit{x}}^{\mathbf{+}}\mathbf{=}{\mathit{d}}_{\mathit{y}}^{\mathbf{+}}\mathbf{=}\mathbf{7}\mathbf{/}\mathbf{4}$ , and ${\mathit{\nu }}_{\mathit{x}}^{\mathbf{+}}\mathbf{=}{\mathit{\nu }}_{\mathit{y}}^{\mathbf{+}}\mathbf{=}\mathbf{2}\mathbf{(}\mathbf{1}\mathbf{-}{\mathit{\nu }}_{\mathbf{0}}^{\mathbf{+}}{\mathbf{log}}_{\mathbf{2}}\mathbf{cos}\frac{\mathit{\pi }}{{\mathit{k}}^{\mathbf{+}}}\mathbf{)}$ , ${\mathit{\nu }}_{\mathbf{0}}^{\mathbf{+}}\mathbf{\to }\mathbf{+}\mathbf{\infty }$ .