I have an undergrad in math (not physics), and I'm in a physics grad program. This text was an absolute lifesaver. It's a beautiful book—very readable and a manageably comprehensive introduction. It doesn't cover everything in a larger book (no book covers everything anyway), but for folks with linear algebra and calculus in their background (and ideally but not necessarily some sense of classical mechanics), it's something you can work through on your own or with a friend. I loved it and look forward to reading other books in this series.