          If the user sets TOL &gt; 0, then the given value of TOL is
          used as an absolute tolerance: an eigenvalue i and a
          temporarily fixed eigenvalue 1 (represented by the first
          element of the current trailing pair of submatrices to be
          reduced) are considered to belong to the same cluster if
          they satisfy the following "distance" condition

            | lambda_1 - lambda_i | &lt;= TOL.

          If the user sets TOL &lt; 0, then the given value of TOL is
