best book ever??? maybe...do you do applied math for a livin' like me part of the time...this is a classic text that can help you...no matter what your level of mathematical sophistication...I love it and have taught from it...I had an amazing teacher(s) that taught from it...Thank you Dr. Nemat Nassar and the late great Si Rand...who taught me so much applied math and physics in grad school..scholar and all round great mench...RIP ...i miss talking to you quietly...ok back to the book...if you need a primer on pde's this it...you can prove orthoganality and the uniqueness of solution...thank you dr. ghassan kassab for helping me with this (one of dr fung's academic sons....one of many that I am grateful too...
Really good introductory book in the theory of partial differential equations and the most important methods of solving them (pretty much: seperation of variables). Ideal for self-study.