Question regarding eigenvalues

The macro


const int N = 3;
double e[N*N] = {
1, 4, 5,
4, 2, 6,
5, 6, 3

TMatrixDSym moo(N, e);
TMatrixDSymEigen me(moo);

TVectorD eigenval = me.GetEigenValues();
TMatrixD eigenvec = me.GetEigenVectors();


works fine. It produces moo which is a symmetric matrix from vector e. What changes should I be making if I already have a symmetric matrix Q, so that I can get eigenvalues of Q. thanks for your help.

I believe basically I am asking is that if I create an object

TMatrixDSym eig(chan*(2L+1),chan(2*L+1));

how can I fill it with another matrix Q. I believe I have to use Use, I am not sure how.