In reply to Siladittya Manna.

You clearly have a lot of questions. I recommend you post to a NumPy discussion forum because I am sure that someone has already written Python code for this.

You have found the largest and smallest eigenvalues by using the power method. You might be able to get the second largest/smallest, but probably not many more. If (lambda, v) is the largest eigenpair, then defining C = A - lambda*v*v` is called "deflation." You can show that the eigenvalues of C are 0 and the nondominant eigenvalues of A. Thus you can apply the power method to C to find the second largest eigenvalue of A. However, a naive implementation of this method is numerically unstable. Google "stability of deflation for eigenvalues." Thus you can rarely continue beyond the second step without losing accuracy.