I am new to eigen. Could you tell me why the following piece of code gives an error?

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

using namespace Eigen;
using namespace std;

int main(){
   int nStates = 5;
   MatrixXd B = MatrixXd::Random(5,5);
   VectorXd ss(nStates);
   ss << 22,123,123,123,1211;
   MatrixXd bb = ss.asDiagonal();
   cout<< B + ss.asDiagonal() ;

}


Here is the error I got
[bug] error: invalid operands to binary expression ('MatrixXd' (aka 'Matrix<double, Dynamic, Dynamic>') and 'const DiagonalWrapper<const Eigen::Matrix<double, -1, 1, 0, -1, 1> >')
cout<< B + ss.asDiagonal() ;
~ ^ ~~~~~~~~~~~~~~~[/bug]

However when I replace the

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cout << BB + ss.asDiagonal()

by

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cout << BB + bb

it works.

This is a non supported operation. You can only combine dense and diagonal matrices trough products or compound assignments:

B += bb.asDiagonal();
B -= bb.asDiagonal();