code: public SymmTridiagEVD factor(SymmTridiagMatrix A)
              throws NotConvergedException {
          if (A.numRows() != n)
              throw new IllegalArgumentException("A.numRows() != n");
  
          intW info = new intW(0);
          LAPACK.getInstance().dstevr(job.netlib(), range.netlib(), n,
                  A.getDiagonal(), A.getOffDiagonal(), 0, 0, 0, 0, abstol,
                  new intW(1), w,
                  job == JobEig.All ? Z.getData() : new double[0],
                  Matrices.ld(n), isuppz, work, work.length, iwork, iwork.length,
                  info);
  
          if (info.val > 0)
              throw new NotConvergedException(
                      NotConvergedException.Reason.Iterations);
          else if (info.val < 0)
              throw new IllegalArgumentException();
  
          return this;
      }
docs: Computes the eigenvalue decomposition of the given matrix
  
  @param A
  Matrix to factorize. Overwritten on return
  @return The current eigenvalue decomposition
  @throws NotConvergedException