Calculus

• Fast Fourier Transform - Article in MathWorld.
• Fast Fourier Transforms - Survey and history of FFT algorithms from Wikipedia.
• An Introduction to Fourier Theory - A mathematically inclined introduction with illustrations and explanations of related theorems, its properties and numerical methods for calculating transforms.
• Introduction to the Fourier Transform - Notes on applications to Image Processing.
• Mathematics of the Discrete Fourier Transform (DFT) - Notes by Julius O. Smith III, Stanford.