Ellipticity of the PNFW mass distribution ε_Σ from the elliptical fit (, solid lines) and GK (, dashed lines) methods, as a function of the parameter ε for four values of , calculated at the tangential critical curve (R_λ = ∞) at x₂ = 0. The dotted line in the upper left panel corresponds to the ellipticity of the lensing potential ε_ϕ(ε), Eq. (15). The dot-dot-dashed line shows the ε_Σ = ε line to guide the eye. The vertical dot-dashed lines show the values of .