Eigenvalue and eigenvector

[mrsh]

Hi,I would like to ask about eigenvalue and eigenvector ,
I manually calculate eigenvalue for this matrix [5,1,-2,2] and the answer are 3 and 4 . However when I run this coding the output give the eigenvalue 1 and 6.

 Matrix2f A;
	A << 5, 1, -2, 2;
	cout << "Here is the matrix A:\n" << A << endl;
	SelfAdjointEigenSolver<Matrix2f> es(A);
        cout << "The eigenvalues of A are:"          << endl << es.eigenvalues() << endl;
	cout << "The matrix of eigenvectors, V, is:" << endl << es.eigenvectors() << endl << endl;

I run the code from
https://eigen.tuxfamily.org/dox/group__TutorialLinearAlgebra.html
title computing eigenvalues and eigenvectors.

[Michael37]

What, exactly, is your question?

Are you looking for confirmation of the answers?
Or are you looking for help with coding?

The answers you calculated manually seem to be correct. I confirmed them with another program: Eigenvalue and Eigenvector Calculator ( http://www.akiti.ca/EigR12Solver.html )

The output from this program is

The eigenvalues follow: 

4
3

Error Code: -1

The eigenvector matrix follows: 

0.7071067811865475     -0.4472135954999581     
-0.7071067811865475     0.8944271909999157     

Commercial programs like MATLAB, MathCAD, Maple, etc. would probably confirm these numbers too. However, I am not familiar with the programs posted on the tuxfamily site, so cannot comment about why their results differ.

[mrsh]

My question is why the coding above give different value of eigenvalue