Learning math is a headache. You have to learn everything about mathematics, including signals and systems, because in the big environment of the University of Posts and Telecommunications. It's hard to say it's difficult, but it should be said that it's difficult. There are too many classes to fail, and almost every door has room to fail. If you don't really love math and analysis, and you don't want to be a master of four years' study in college, be careful. There are not many girls in the School of Mathematics and Science. If you want to get a job, you should mainly look at yourself and your family. There are many postgraduate entrance examinations in the School of Mathematics and Science, partly because of poor employment.