 diagonal elements are not reordered;
          = 'S':  The diagonal elements are reordered before each
                  step of reduction, so that clustered eigenvalues
                  appear in the same pair of blocks.
          = 'C':  The diagonal elements are not reordered, but the
                  "closest-neighbour" strategy is used instead of
                  the standard "closest to the mean" strategy (see
                  METHOD);
          = 'B':  The diagonal elements are reordered before 