Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Very nice book on variational calculus

This book is a more thorough treatment of the calculus of variations than some of the other books on the subject that you could buy. It's bit more expensive... I especially reccomend this book if you like Sagan's other book "Boundary and Eigenvalue Problems in Mathematical Physics". If you like his style of writing, and I do, he again shows nice touch of explaining the material in writing and then with examples. A good book with a nicely written and more thorough treatment of the subject (unless you want a full price text that is)..