What's the highest-level math you've used in the real world? What did you need it for? Where did you learn it (in school, by yourself)? (Incidentally, I do mean in a *programming context*, as this is a programming website.)

Note: I'm not wondering if mathematics is necessary for programming or the relationship between math and programming, and I'm not trying to figure out how much math to learn myself. Those are all good questions, but I was just wondering what the highest-level math *you personally* used in the real world. (You can decide what "highest-level" means for you personally as well.)

Perhaps it was for a domain-specific application. So your answer might be:

- Computing projections and intersections in computer graphics
- Quaternions because you work with 3-d rotations
- Runge-Kutta or the finite element method for some differential equations
- Fourier transform for some signal processing
- Nothing beyond bit operations
- "None at all"

I don't know! But I'm interested.