I love Linfeng Li. He’s a super cool and funny guy. Only problems with lecture are his accent can be a bit rough to understand and he tends to copy the textbook for the most part (though he’ll try to answer any questions). The weekly homework’s tend to be pretty short, and the quizzes are extremely easy (there are three during discussion weeks 3 6 and 9). The midterms were rough for me as I made a small mistake on each one that really messed up my score. He was accommodating and gave me a few points back after I explained myself but I ended up dropping that one anyways(he can drop your lowest midterm and increase the weight of the final). The final was extremely fair and very similar to resources he provided in the weeks leading up to it. Everyone I know who prepared well did well on the final, so don’t be disheartened if the midterms are a bit rough. Live Love Lifeng

The teaching style of Professor Li is very fast-paced as is the nature of the course. To me, I would need to supplement the lectures with the textbook and other resources to fully understand how to do the homework problems. This made some problems in the homework quite frustrating to do. I feel like it would be better if the professor went over more example problems or at least similar problems to what we see in the homework. However, if you do need help with the homework, the professor sticks around after class and talks through some of the concepts that students may find challenging which is certainly a nice thing to do. The professor also doesn't record any of the lectures or post notes to Canvas (he only airdrops them) which is a little inconvenient especially when you have an unlucky seat for the week and someone in the first row blocks the board with their head. Overall, the clarity of the lectures could benefit from more examples and fewer proofs but Fall 2023 is also the very first time this professor is teaching this course so it can only improve from here.

Math 31B is hard no matter who you take it with. Professor Li was a really funny guy, but he can be kind of hard to understand. When you ask a question in class he will pretty much never understand what you are trying to ask but its ok. My TA was even harder to understand and made me even more confused so I stopped going except for the quizzes (which were super easy). The midterms were hard and required a lot of creative thinking to solve the problems. This class was brutal and I spent so long studying for each exam and for the most part, it paid off once you figured out how he tested. He moves very fast so make sure you pay attention the entire time or else you're going to be very confused. He is really responsive to his emails as well even responding to me at 9pm the night before the final which was really nice.

Professor Li is a great professor teaching-wise; he uses examples that are clear and his teaching style is really nice (he screenshares his iPad as he takes notes on it), and he posts his notes online if you miss class for whatever reason. However, this class is generally difficult and personally for me (someone who struggles with math), it took an insane amount of effort. I did ok on the first midterm (B+), did extremely well on the second (A+), and completely bombed the final (got a F). There are quizzes in discussion on Weeks 3, 6, and 9; and midterms on Weeks 4 and 8, so it feels like there's a test almost every other week. While the quizzes were manageable, it felt like the final was incredibly difficult and nothing like the practice problems. (I also can't tell if the problem lies with me or the test). However, Li is a great professor and I recommend taking the class with him! I enjoyed his class and felt motivated to attend; I just suck at math unless I make it my sole focus and concentration and ignore my other classes 😫

If I'm going to be completely honest, I've never struggled in a class like I️ did in 31B with Li. I️ took AP Calc AB in hs so I️ passed 31A with flying colors the quarter before. Unfortunately, this class hit me like a TRUCK. Professor Li is a new teacher so I️ want to offer understanding, but it's pretty obvious that he isn't skilled in teaching a 300 person class. Li's accent can be a bit hard to understand, and he often explained things in ways that made sense for his brain but not the class as a whole. He doesn't record lectures either which makes attendance extremely important - even though it's so hard to follow along at the speed he teaches/writes. Li isn't necessarily a bad teacher, but I️ wouldn't recommend taking 31B with him unless you've taken BC and know all the material already.

professor li does not record class which is unfortunate but i will admit he has a very organized and convenient system. if you get his class you will see what i'm referring to since he uses and updates this webpage and has a chart that he updates every day attaching the exact notes he creates during class, the topics covered that day, and the homeworks assigned. i think the biggest let down of this course was the hard exams. i found the exams were harder than what we expect but SOLELY DUE TO BASIC ARITHMETIC. i understood all of the concepts and was able to apply it but got so many points taken off due to small errors. thankfully he did adjust thresholds and raise my grade but i remained in the b range. he's a chill dude and he's funny without even trying. i don't think he was a bad professor, but i would've taken him as a second option if i could.

The course was enjoyable overall and well organized. However, I don't think I learned as much as I could have for a few reasons: First, the class was much too computational for my taste, and felt more like a sequel to 33A than to 115A. Second, proofs often relied very heavily on unproven lemmas, where all the work lies in the proof of the lemma. We essentially skipped the proofs of most major results in this manner. For instance, our "proof" of the Spectral theorem presumed the existence of an orthonormal basis of eigenvectors, and the only work we did was finding the matrix decomposition corresponding to this basis. Despite these shortcomings, I still enjoyed the lectures as they were very clear and easy to follow. Homework and exams were also very well-made.

Overall, Professor Li was a very kind person. He always responded to emails in a timely manner and would stay after class to answer questions. I took Math 31A before taking this class and I thought it would've been similar. Unfortunately it was not and 31B was almost 10x as difficult. Honestly, I don't even think it was Professor Li's fault because 31B is notoriously known as a difficult class. That being said, Professor Li's exams were HIGHKEY difficult and the TA's graded extremely harshly. I literally had to beg on my knees for 2 points back on a few midterms. The midterms were graded out of 40 so it was weighed in a odd manner. The average for the midterms and finals were around 60-70%. Thankfully, Professor Li curved SO MUCH I went from a 85% (B) to a A- LIKE HELLO. BLESS LINFENG LI FOR HIS CURVE BUT I WILL NEVER BE TAKING ANOTHER MATH CLASS EVER IM SCARRED. GOD BLESS

I unfortunately cannot recommend Professor Li for 31B. If you were unable to take BC in high school (my school didn't offer it), then find a different professor. Honestly, his lectures aren't too bad, and he has funny moments. Overall, however, his tests are unnecessarily hard. You can do great on the homework and understand the lecture but Li does not help you know what's going to be on the tests at all. Our final in particular was way more difficult than anything he had taught us. The only reason I didn't fail the class is because he was forced to curve ending grades BECAUSE of his final's difficulty. A girl left crying, everyone was there the entire 3 hours, and his midterms weren't much better. I think if you already go in with a strong understanding of the material you will be just fine, but if not, definitely find someone else.

Prof aight, class terrible. Not much homework, but the few problems rly difficult. One of the few classes where I got significant amount of points taken off hw. Every example shown in lecture is 10x easier than whatever is in hw and especially on exams. That is why going to office hours is necessary, but there is only 1/week so it is kind of hard to go through everything. Also NO flash card, so we had to memorize the 8 tests or whatever. Since exams were so bad (avg for final was 69%), he lowered the threshold by a lot. (My 83% was a B+).