code: public static EVD eigen(Matrix A, int k, Ritz ritz, double kappa, int maxIter) {
          return eigen(A, k, ritz.name(), kappa, maxIter);
      }
docs: Find k approximate eigen pairs of a symmetric matrix by the
  Lanczos algorithm.
  
  @param k Number of eigenvalues of OP to be computed. 0 < k < N.
  @param ritz Specify which of the Ritz values to compute.
  @param kappa Relative accuracy of ritz values acceptable as eigenvalues.
  @param maxIter Maximum number of iterations.