How to define Vector with template using Eigen library?

Question

I know Eigen use Matrix to represent vector, but for templatrized vector, what I know is to use something like

Eigen::Matrix<T,3,1> v;

Is there something like Eigen::Vector<T,3> for use?

Answer 1

All Eigen::Vector types are mere typedefs. All C++ standards prior to C++11 don't support templated typedefs (aka alias) and Eigen is written to support also older standards than C++11.

If you are using C++11 you can define your own templated Vector alias

template <typename Type, int Size> using Vector = Eigen::Matrix<Type, Size, 1>;

and then use it the way you want

Vector<double, 10> vec;

By the way, Eigen has typedefs for vector sizes between 2 and 4, i.e. Eigen::Vector2d, ..., EigenVector4d. The same typedefs exists for floats with the suffix f and integer i and for complex numbers cd, cf.