Methods of Theoretical Physics, Part I (International Series in Pure and Applied Physics)

this is another in the long line of math methods books that plague/bewilder/frustrate physics undergrads

standard: https://www.amazon.com/Mathematical-Methods-Physicists-Seven...

gentler: https://www.amazon.com/Mathematical-Methods-Physical-Science...

another recent addition: https://www.amazon.com/Mathematical-Tools-Physics-Dover-Book...

"purer" than the rest: https://www.amazon.com/Mathematical-Physics-Chicago-Lectures...

"more fun" than the rest: https://www.amazon.com/Geometry-Physics-Introduction-Theodor...

this pair is probably the most rigorous and difficult of the bunch (at least from what i remember):

https://www.amazon.com/Classical-Mathematical-Physics-Dynami...

https://www.amazon.com/Quantum-Mathematical-Physics-Walter-T...

and the grand-daddy of them all

https://www.amazon.com/Methods-Theoretical-Physics-Internati...