Figure 1

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 ${\mathit{k}}_{\mathit{x}}^{\mathbf{\pm }}\mathbf{=}{\mathit{k}}_{\mathit{y}}^{\mathbf{\pm }}\mathbf{=}\mathbf{3}$ , ${\mathit{d}}_{\mathit{x}}^{\mathbf{-}}\mathbf{=}{\mathit{d}}_{\mathit{y}}^{\mathbf{-}}\mathbf{=}\mathbf{3}\mathbf{/}\mathbf{4}$ , ${\mathit{d}}_{\mathit{x}}^{\mathbf{+}}\mathbf{=}{\mathit{d}}_{\mathit{y}}^{\mathbf{+}}\mathbf{=}\mathbf{5}\mathbf{/}\mathbf{2}$ , ${\mathit{\nu }}_{\mathit{x}}^{\mathbf{\pm }}\mathbf{=}{\mathit{\nu }}_{\mathit{y}}^{\mathbf{\pm }}\mathbf{=}\mathbf{12}$ , ${\mathit{\nu }}_{\mathbf{0}}^{\mathbf{\pm }}\mathbf{=}\mathbf{21}$ .