 name="Method"><B><FONT SIZE="+1">Method</FONT></B></A>
<PRE>
  The routine computes the roots (r1 and r2) of the real quadratic
  equation
          2
     a * x  + b * x + c = 0

  as
          - b - SIGN(b) * SQRT(b * b - 4 * a * c)             c
     r1 = ---------------------------------------  and r2 = ------
                           2 * a                            a * r1

  unless a = 0, in which case

          -c
     r1 = --.
           b

  Precautions are taken to avoid overflow and underflow