Deng is actually a visiting professor from Stony Brook, but I am writing this review in case Columbia decides that inviting him back would be a good idea.
He is the worst professor I have ever had. I was excited to take numerical methods, but this guy does not teach. I could go on and on but I think this summarizes it: He shows you Wikipedia pages in class. He'll lecture on say, linear algebra, from an analytical standpoint, without ever getting into the NUMERICAL methods. The lectures are completely devoid of content and it shows in the fact that half the class is routinely absent; on quiz days, there is a marked uptick in the number of people in the room for the second half of class (quizes were given in-class for the second half of our double-session class).
If you see Deng listed as the professor for a class you want to take, run.