Here is a collection of nice tutorials and important papers that I have personally found useful when trying to understand certain concepts in mathematics and physics. Some of these concepts are used in this project, while the others keep me awake at night.

Mathematics:

Understanding the Fourier Transform (by Stuart Riffle)
The Discrete Variational Approach to the Euler-Lagrange Equations (by Y. Wu)
Group Theory: A Tutorial (by Michael Leyton)

Physics:

Elementary Principles in Statistical Mechanics (by Josiah W. Gibbs)
Problems in Physics with Many Scales of Length (by Kenneth G. Wilson)
Statistical Mechanics: Entropy, Order Parameters, and Complexity (by James P. Sethna)
Order Parameters, Broken Symmetry, and Topology (by James P. Sethna)
Scaling theory of continuum dislocation dynamics in three dimensions: Self-organized fractal pattern formation (by Yong S. Chen et al.)
Simple Lessons from Complexity (by Nigel Goldenfeld and Leo P. Kadanoff)
Renormalization Group Theory: Its Basis and Formulation in Statistical Physics (by Michael E. Fisher)
The Renormalization Revolution (by Leo P. Kadanoff)
Overcoming misconceptions about configurational entropy in condensed phases (by Evguenii I. Kozliak)
Insight into Entropy (by Daniel F. Styer)
Studies of Nonlinear Problems (by Enrico Fermi, John Pasta, Stanislaw Ulam and Mary Tsingou)
Defects in Crystals (by John W. Morris, Jr.)