The University's numbering scheme has been employed to indicate very roughly the level of the graduate courses. The 400 series is "at the master's lever," which means in practice that such courses are normally taken by students in their first two or three semesters of graduate work. The 500-level courses are more likely to be taken by second- or third-year students. In some cases, a sequence spans the two levels: 407-408-509-510 is a complete quantum mechanics sequence, 415-516 covers all of graduate electromagnetic theory, and 418-519 is a two-semester sequence in statistical mechanics.
The Graduate Bulletin lists several courses called "Special Topics in ..." whose numbers are of the general number 5X4. These courses are given on demand and consist, usually, of a continuation or specialization of the material in courses 5X1, 5X2, and 5X3. The current listing of instructors should be consulted to determine which of these courses are being offered.