Professor Yao is your average Joe: not too bad, but not great either. His lectures are pretty dry, so it's hard enough staying awake for the full 2 hours, but he does write a lot of equations and derivations on the board.

The material during the first half of the course wasn't terribly difficult, but I felt like after the midterm, the material got immensely harder day after day. I couldn't really learn much from his lectures after the second midterm since I was already swamped with work from other classes.

Sometimes, I feel like whenever a student asks him a question, he doesn't exactly understand it, so he tries to come up with an answer that doesn't exactly answer the question.

His homework assignments weren't difficult to begin with, but they got increasingly harder week after week. He said that if you can do the homework by yourself without looking at a solutions manual, you should be able to do well on his exams. That's not necessarily the case because I felt like the latter homework assignments was essentially copying equations from the textbook.

As for the exams, they're not terribly difficult, but they're definitely not easy. I got average on both the midterm and the final, but I felt like I could have scored more had I spent more time on this course.

His final exam was kind of unique: the first 90 minutes was closed-book closed-notes while the latter 90 minutes was open-book open-notes. However, the first part of the exam was significantly easier since it focused more on Fourier Transforms, which were primarily covered in the first half of the course.