Harry Hochstadt: 2 books

Modern approach to differential equations presents subject in terms of ideas and concepts rather than special cases and tricks which traditional courses emphasized. No prerequisites needed other than a good calculus course. Certain concepts from linear algebra used throughout. Problem section at end of each chapter.

Comprehensive textbook provides both mathematicians and applied scientists with a detailed treatment of orthogonal polynomials, principal properties of the gamma function, hypergeometric functions, Legendre functions, confluent hypergeometric functions, and Hill's equation. Lucid and useful presentations for anyone working in pure or applied mathematics or physics.