Not only older issues of the Numerical Recipes books, but also classics such as
Handbook Abramowitz and Stegun, Handbook of Mathematical Functions (10th corrected printing, 1972)

Bateman, Erdelyi et al. (Bateman Manuscript Project)
Higher Transcendental Functions (vols. 1, 2, and 3)

and
Encyclopaedia Britannica the great 11th Edition (1911)

Found via https://www.hpmuseum.org/forum/thread-16251-post-142741.html#pid142741

Blog describing many cases where algorithms with quadratic complexity appear, almost always unintentionally.

Matlab implementation of the Durand-Kerner algorithm to compute the roots of a polynomial.

This is just an example, the site contains a large number of documents written at MIT.

Converting color temperature (Kelvin) to RGB.
The algorithm provides a high-quality approximation, but it’s not accurate enough for serious scientific use. It’s designed primarily for photo manipulation – so don’t try and use it for astronomy or medical imaging.

Interesting algorithm to invert functions, implemented in Common Lisp.

MIT Photonic Bands (MPB) electromagnetic eigenmode solver Meep finite-difference time-domain simulations Harminv extraction of complex frequencies and amplitudes from time series libctl Scheme/Guile-based scripting of scientific code (used as the interface for MPB and Meep). h5utils visualization of HDF5 data files NLopt nonlinear optimization library implementing many different optimization algorithms Cubature code for adaptive multidimensional integration of vector-valued integrands via the Genz-Malik algorithm. Faddeeva_w code to compute the complex error function (Faddeeva function).

Windows applications or source code for various numerical algorithms, with emphasis on polynomial root finding. Some algorithms can be used via a web interface.

Some interesting code (mostly C++) for numerical integration, special functions, polynomial roots etc.

Description of a fractal related to the Mandelbrot set and how it was rendered to a high resolution image.