What is a good open source C/C++ math library that supports vector math and complex numbers?

Question

I am working on a project that needs vector math and complex numbers.

I am looking a for a good open source API that supports C/C++ and hopefully has decent performance.

I can write these functions myself but it will be ugly and slow.

Answer 1

I regularly use Sony Vector Math library bundled with bullet physics. It's fast has many linear algebra algorithms.
For complex numbers you can simply use std::complex