Boundary-Consistent L1–Legendre Spectral Approximation of Nonlinear Caputo Reaction–Diffusion Problems with Integral Constraints
This paper develops and verifies a boundary-consistent L1–Legendre spectral method for nonlinear Caputo reaction–diffusion equations with integral constraints, demonstrating that directly assembling the strong-form operator is essential to avoid error plateaus and achieve machine-precision convergence where conventional derivative stiffness formulations fail.