To tell the truth, it is still difficult to transform from other disciplines to postgraduate mathematics, which is not recommended. The first test subjects of mathematics for postgraduate entrance examination are politics, English and two specialized courses, and the second test subjects also include probability theory, differential equations and other subjects, depending on the school.
To tell the truth, there are many undergraduate students majoring in mathematics who take postgraduate entrance examinations in the schools around me, which has many advantages over the cross-examination and if you want to take the cross-examination, your score requirements are higher than those of students who do not take the cross-examination.
Financial and electrical engineering and its automation, if you really choose, the latter will be easier to wash.