Λ_n = ||L_n|| operator-norm of n-point interpolation projection bounds approximation error: ||f - p_n|| ≤ (1+Λ_n) E_n(f). Equispaced nodes: Λ_n grows exponentially (Runge phenomenon); Chebyshev nodes: Λ_n ~ (2/π) log n optimal.
Λ_n = ||L_n|| operator-norm of n-point interpolation projection bounds approximation error: ||f - p_n|| ≤ (1+Λ_n) E_n(f). Equispaced nodes: Λ_n grows exponentially (Runge phenomenon); Chebyshev nodes: Λ_n ~ (2/π) log n optimal.