Great professor. The class has a lot of confusing material that demands a lot of time and thought, but Prof. Sahai leads students through a kind of investigation, piecing together the foundations of automata theory one step at a time. I've had a lot of other professors try this and fail, because they're still fundamentally focused on textbook material, but Sahai will entertain every passing inquiry, sometimes coming to new proofs and conclusions not found in any of the provided texts.

In a similar vein to his lectures, assignments and exams will ask you to consider hypothetical machines and scenarios and make judgments about them. Other professors teaching this course might simply ask for the FSM diagrams of regular expressions, but his exams aim to challenge and entertain based on the approaches outlined in class. The final is take-home, so you'll have plenty of time to ponder and puzzle over the provided problems, which will range in difficulty from the trivial to the nearly incomprehensible. Mental blocks can be resolved by attending office hours (TA or professor, though be warned Sahai himself tends to shy away from a direct answer, preferring to clarify concepts he thinks you might not have understood) or collaborating with other students (for the assignments, not the final.)

Sahai might stress the difficulty of the class's grading at the beginning of the quarter, but extra credit opportunities come by the boatload if you're willing to participate, and is applied after grades (without extra credit) are curved.

Good

I took this class in Winter 2012. This class is extremely challenging. However, I would say I learned the most in this class out of any other class.

The review about lectures sucking is completely wrong. I guess whoever wrote that review only went to lecture once when we had a bad day. Sahai encourages questions in lecture by offering extra credit points for participating (1/4 percent per attempted answer) and very often the class as a whole will help solve the problem or derive the theorem's proof that Sahai is focusing on that day.

The homeworks take about 10-16 hours a week. Start early! Sahai and the TA (Abishek) often repeat this and say that the only way to solve these problems is to read the book, go to lecture, collaborate with your classmates (but not plagiarize), and repeatedly bang your head against the problems until you have an epiphany. It's tough, but they're right. Once you solve a problem, you gain a pretty profound understanding of the material, and that's a really satisfying feeling.

With that said, some of the homework problems are indeed rigorous proofs. Sahai warned us that the winter offering of CS 181 is a more challenging offering, and that we are expected to have knowledge of proofs. If we don't, he gives a link/guide on how to write proofs and different methods, such as proof by contradiction (the most common one in this class; just about every proof is with this method), unwinding the definition, proof by induction (also a common method), applying the Pigeonhole Principle, and so on. In addition, all proofs that Sahai does in the class and that Abi does in discussion are rigorous proofs, so you can learn by their examples.

Discussion was an extension of lecture where new material was taught in addition to clarifying old topics. Abi also went over the homework a little bit but rarely gave hints.

The midterm was easier than the homework, because we only got 2 hours to do it in class. The final was very challenging, but not unreasonable, and it was take-home format so we were given a week to do it. There is no collaboration allowed on the final.

Office hours were very effective. No hints as to the kind of test problems to expect were given during OH.

His curves are not that generous. I would say that he only gives about ~15% A's; even though everything busts their butt, most people will get B's. If you are looking for a cakewalk class, don't take Sahai. If you are looking to learn a lot, and maybe get a B even if you worked really hard, then take this class!

He's a okay lecturer, or whatever, but he often asks for class input. The class usually just gives him blank stares, and when someone does answer his question, they are wrong 100% of the time. When he tells them that they are wrong, he says "No, that's not quite what we're looking for." And that's it. Occasionally, he'll say "Someone already said that" if you unintentionally paraphrased what someone else said, but the fact of the matter is that he provides little to no reasoning as to how we are supposed to correctly approach these problems. I, for example, came into this class with no experience with proofs and I can safely say that, having shown up to class every day, I still have no clue as to what makes a proof a proof. Is it the way I phrase it? What makes statement A any less "proofy" than statement B? He never addressed these problems in class, even though there is a large chunk of the class (75%+) that still doesn't know how to do proofs properly.

Honestly, I think the reason his rating of "Is concerned" is just because of the way he talks to students. I, however, find it condescending, especially when he outwardly laughs at what the students suggest for proofs. Altogether, I would have gladly taken the class from a clam rather than from Sahai, as at least a clam wouldn't laugh at me when I make a suggestion for a proof.

Absolutely fantastic professor. Every lecture was well prepared, organized, and interesting. Class was difficult but so interesting that students were encouraged to work their hardest. I would love to have this teacher for more classes.

Prof. Sahai is a very good lecturer and has made CS 181 a breeze for us. He does challenge his students but he makes sure everyone can succeed if they want to.