eigen/doc/examples/TutorialLinAlgInverseDeterminant.cpp

#include <iostream>
#include <Eigen/Dense>

int main()
{
   Eigen::Matrix3f A;
   A << 1, 2, 1,
        2, 1, 0,
        -1, 1, 2;
   std::cout << "Here is the matrix A:\n" << A << std::endl;
   std::cout << "The determinant of A is " << A.determinant() << std::endl;
   std::cout << "The inverse of A is:\n" << A.inverse() << std::endl;
}