The best professor I've had at Columbia by far.
He's everything a math professor should be, clear concise notes, very approachable and helpful during class and during office hours. Very friendly and mature, despite how young he is, but expects a lot from students. While Calculus IV is a computational math course, he does provide some theory and interesting examples, with proofs and complex analysis. That being said, the class is Difficult, but fair, homework problem sets are very long but preparatory for the exams. Expect to devote a lot of time for this course. The tests are of fair difficulty and grading, but the final exam was particularly difficult, and long for the allotted time. Grades are slightly curved though.