code: public static double eigen(Matrix A, double[] v, double tol, int maxIter) {
          return eigen(A, v, 0.0, tol, maxIter);
      }
docs: Returns the largest eigen pair of matrix with the power iteration
  under the assumptions A has an eigenvalue that is strictly greater
  in magnitude than its other eigenvalues and the starting
  vector has a nonzero component in the direction of an eigenvector
  associated with the dominant eigenvalue.
  @param A the matrix supporting matrix vector multiplication operation.
  @param v on input, it is the non-zero initial guess of the eigen vector.
  On output, it is the eigen vector corresponding largest eigen value.
  @param tol the desired convergence tolerance.
  @param maxIter the maximum number of iterations in case that the algorithm
  does not converge.
  @return the largest eigen value.