How to calculate eigenvalues in ROOT?

My matrix is 15x15.
I want to call this ROOT function from c++.

Which Root function?Please be more specific.



Have a look at

const TMatrixD EigenVectors(TVectorD& eigenValues) const or
const TMatrix EigenVectors(TVector & eigenValues) const :

TMatrixD a(15,15);
TVectorD eigenVal;
const TMatrixD eigenVec = a.EigenVectors(eigenVal);

At the moment vector a has to be symmetric !