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Introduce a method which can prove some function can be approxed by other functions by using Hahn-Banach Theorem and Riesz Representation Theorem, then use this method to prove Runge theorem.

Note about the error analysis of (linear) finite difference method for BVP and IVP.

Some note about Fourier spectral method (unbounded grid and periodic grid).

Some note about Green’s function.

百年孤独 — 加夫列尔·加西亚·马尔克斯， 1967年

A brief introduction to Fourier transform and Fourier series in both continuous and discrete case.

简要介绍Abel群上的Fourier变换，以此为基础给出FFT的基本思想。