eigen@3 for Mac

Eigen is a C++ template library for linear algebra, aimed primarily at developers who need to work with matrices, vectors, numerical solving, and related algorithms. It wraps common linear algebra operations into easy-to-use template interfaces, allowing C++ programmers to perform matrix operations and numerical computation tasks in their projects without implementing the underlying mathematical logic from scratch. Because it is provided in template form, it is better suited to developers with some C++ foundation who want to integrate mathematical capabilities directly into engineering code, and it is commonly found in scenarios such as scientific computing, graphics, and robotics that require frequent linear algebra operations. When used, it is typically included in the form of header files and works together with the compilation toolchain.