Chebyshev Spectral Differentiation via Fast Fourier Transform
Consider the function with derivative . This Demonstration uses Chebyshev differentiation via Fast Fourier Transform (FFT)  to estimate at the Chebyshev–Gauss–Lobatto points. You can change the number of interior points, . The error (i.e., the difference between the exact and approximate values of ) decreases for large values of .