N
          E1 and E2 contain either the real eigenvalues or the real
          and positive imaginary parts, respectively, of the complex
          eigenvalues of the selected 2-by-2 diagonal block of A.

</PRE>
<B>Error Indicator</B>
<PRE>
  INFO    INTEGER
          = 0:  successful exit;
          &lt; 0:  if INFO = -i, the i-th argument had an illegal
                value.

</PRE>
<A name="Method"><B><FONT SIZE="+1">Method</FONT></B></A>
<PRE>
  Let A1 = ( A(L,L)    A(L,L+1)   )
           ( A(L+1,L) 