During the first year, Part IA, the schedule of courses is quite rigid, providing much of the basic knowledge requisite for mathematics, including algebra, analysis, methods in calculus, and probability. The second year, Part IB, contains no mandatory content but it is recommended that students do particular courses as they are an essential prerequisites for further courses. A range of pure courses, such as geometry, complex analysis and a course studying group theory, rings and modules are on offer as well as applied courses on electromagnetism, quantum mechanics and fluid dynamics. In Part II, students are free to choose from a large number of courses over a wide range of mathematical topics, these are separated into more accessible C courses and D courses with are more involved. Some students choose to exchange 25% of the first year mathematics options in exchange for the Physics option of first year Natural Sciences Tripos with the possibility of changing to Natural Sciences at the end of the first year.