#include <iostream>#include <Eigen/Dense>intmain(){Eigen::Matrix2dA;A<<2,1,2,0.9999999999;Eigen::FullPivLU<Eigen::Matrix2d>lu(A);std::cout<<"By default, the rank of A is found to be "<<lu.rank()<<std::endl;lu.setThreshold(1e-5);std::cout<<"With threshold 1e-5, the rank of A is found to be "<<lu.rank()<<std::endl;}