Conceptual

Convergence-Rate Deterioration of Spectral Differentiation for Singular Functions

A pointwise error analysis showing how spectral differentiation of Jacobi (and Chebyshev) polynomial approximations loses accuracy when the underlying function has an algebraic singularity: each extra order of differentiation costs two orders of convergence at the endpoints, one order in the smooth interior, and a parity-dependent or endpoint-dependent amount at the singularity itself, rigorously justifying the error-localization property of Jacobi approximation.