Pit Falls

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Pit Falls

Alignment Issues (crash)

Eigen has made some trade offs in favor of performance that have some costs in the use of the library.

Specifically there are a class of pit-falls related to alignment that are important to understand before choosing Eigen.

You can read more about them here but in short they are:

Header Issues (failure to compile)

Eigen has split the functionality of individual types across header files which can cause confusion. Just because you can instantiate a type does not mean that you have access to all of it's functionality. To concisely illustrate the issue consider the following:

#include <Eigen/Core>
int main()
	Eigen::Vector3d vec1, vec2;
	vec1.cross( vec2 );
	return 0;

Compiling this will an error in line 5 (vec1.cross...):

undefined reference to `Eigen::Matrix<double, 3, 1, 2, 3, 1> Eigen::MatrixBase<Eigen::Matrix<double, 3, 1, 2, 3, 1> >::cross<Eigen::Matrix<double, 3, 1, 2, 3, 1> >(Eigen::MatrixBase<Eigen::Matrix<double, 3, 1, 2, 3, 1> > const&) const'

...because the cross product functionality is in another header(Eigen/Geometry).