How to deal with professors who don't follow the text I'm a first year math grad student. As an undergrad, all my professors followed the given text book closely, making lecture easy to prepare for and very predictable. As a grad student, my professors seem to cover material mostly in the book, but in a different order, with different notation, or different content entirely.
The result is that I have essentially no way to prepare for classes. I can only show up to lecture and hope I can keep up. If I want to review, I can only read their handwritten notes. My understanding is really suffering because I can't reinforce the content by seeing it repeatedly and clearly. I know it's unreasonable to expect professors to merely regurgitate a textbook, but this is how I'm accustomed to learning. What can I do to learn material better in these situations?
Edit: Thank you for the replies. The consensus seems to be that lectures shouldn't reinforce the text. They should provide a bigger picture, a linking of ideas from the expert's point of view, and understanding details is the job of the student on their own time. This makes total sense.
I think my issue comes from spending valuable time studying the book, then having the professor totally skip that topic and go to another, never to mention the thing I spent hours studying. My effort is wasted, and I have to expend double the effort to understand what is covered. It seems like the answer is to just learn what I can and not see that effort as wasted.
If your undergraduate lectures were perfectly predictable, following the book exactly, and you showed up perfectly prepared to each one, then they were actually completely useless. You could have just stayed home and read the book yourself!
At the graduate level, the best practice is to ask the professor for good references, both at the start of the course, and whenever unfamiliar topics come up. You shouldn't expect immediate full understanding from going to lecture; graduate subjects are too deep for that. Treat lecture as an informal invitation to the subject. It's your job to turn that into understanding, by reading from references, doing problems, and asking questions.
Of course, this isn't an excuse for lazy or disorganized teaching. When a professor doesn't follow a book, they could be doing you a great service, by presenting a carefully thought out, alternative view of the subject which will complement existing books. (That's where many textbooks come from in the first place!) But in other cases, they could simply not care much about teaching, and not have any direction in mind.
I've been in classes of both types, and if you're stuck in the latter, it's absolutely essential to get good references to solidify your understanding. In these cases, don't count on the professor to supply them -- if they aren't paying much attention, they're likely to recommend books they used decades ago which are well out of date, or subpar books that they've only heard of, not read. Ask other students, and try resources like StackExchange. You can find good resources for any graduate course in any subject in this way.

I think my issue comes from spending valuable time studying the book, then having the professor totally skip that topic and go to another, never to mention the thing I spent hours studying. My effort is wasted, and I have to expend double the effort to understand what is covered.

If you're planning on doing research later, then effort spent learning core material in standard graduate-level books is never wasted. You can't know in advance what's going to be useful for your research, and often it will turn out to be the core material -- which is why it's the core in the first place. Many times, I've been stuck on a research problem only to find that the right way of thinking about it was in a book chapter I skipped long ago.