Attempt to find the first zero of at the radiative–convective boundary. We consider the typical red giant with M = 1.5 M_⊙, Z = 0.02 on the RGB. Panel a: trend of the evolution of the ψ function at r = R_rad with the eigenvalue λ. The value λ₁ closest to the eigenvalue is indicated by the red vertical line. Panel b: shape of the functions , and ψ_λ1(r, θ) with λ₁ ≃ 7.62, the vertical dashed line indicates the surface. Panel c: magnetic field components with λ₁ ≃ 7.62. Panel d: resulting magnetic field topology with λ₁ ≃ 7.62.