Hi,
I know how to obtain the eigenvalues of a matrix. I need to find the maximum among them and then get its absolute value. How can i do this? I am a newbie to Eigen library. Please help!

If your problem is symmetric, then make sure you are using the SelfAdjointEigenSolver class, and then the eigenvalues are already sorted from the smallest to largest. Otherwise the eigenvalues might be complex, and so you can call .cwiseAbs().maxCoeff() to get the largest in magnitude.