Hi all

I have the following code #include <iostream>
#include <string>
#include <Eigen/Dense>


using std::cout;
using std::endl;
using namespace Eigen;

#define n 5

int main(){
MatrixXd m = MatrixXd::Random(n,n);

cout << m.lu().matrixLU() << endl;
cout << endl;

MatrixXd l= MatrixXd::Identity(n,n);
MatrixXd u= MatrixXd::Zero(n,n);

(l=m.lu().matrixLU().triangularView<StrictlyLower>()) += MatrixXd::Identity(n,n);
u=m.lu().matrixLU().triangularView<Upper>();

cout << l << endl<<endl;
cout << u << endl;

cout << "Are they equal" << endl;
cout << m.lu().permutationP().inverse()*( l*u) << endl;
cout << endl;
cout << m.lu().reconstructedMatrix() << endl;

// cout << m << endl;

cout << endl;


}

when I compute m.lu().permutationP().inverse()*( l*u) shouldn't this be equal to m?

Any thought is appreciated. Thanks!

hm yes, and here they are indeed equal.... what's the matter?

Note that you can also use "m.lu().matrixLU().triangularView<UnitLower>()" instead of adding the identity matrix.