特征向量判据问题

Question

i am using

Eigen::Vector2d vector(1,2)
std::cout << "x" << vector[0] << std::endl;

but this is not working because of invalid overload of cout

But this value should be double or?

Eigen::Vector2d vector(1,2)
double x = vector[0]
std::cout << "x" << x << std::endl;

this works... anyone know why ? Or what i have to do to get the double value back ?

thanks for help

Answer 1

Maybe the result of vector[0] is not double ? Maybe it's some class or a custom type? In the first snippet you've explicitly converted vector[0] to double . If that case, try casting the result in the second snippet:

Eigen::Vector2d vector(1,2);
std::cout << "x" << (double)(vector[0]) << std::endl;