Helpful and organized.

Xu is the most helpful professor I have ever met, he is always open to students' questions. Most important, he is very brilliant and inspiring. As his convention, the first day lecture would mention the tensor which is the content should be learned in UD course, don't be scared, because his homework and exams are quite easier than you expect :)

Prof Xu is nice in person. Reply emails really fast. Yet exams are HARD. Homework not as hard, but some say it isn't close to exam questions. If you get extremely complicated expressions for your answer on exams, do trust yourself. The correct answers often look insane, and you should always attempt every problem cuz graders give partial credit.

Generally clear in the teaching. The class is very theoretical and focuses heavily on simplified models. Doing the homeworks made me very familiar with Mathematica too!

Prof. Xu is a good person. He is always patient in explaining the homework during office hours. His exams are challengeable but I think that will be beneficial to the students who are intended to pursue a career in physics.

Professor Xu is a very nice, caring, and smart person. However his teaching ability isn't really great. Instead of teaching us to understand how and why things were the way they were, we were given equations and simply expected to know how and when to use them. He is always open to questions but his explanations felt like a reiteration of the book