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UTDE2

       DOUBLE PRECISION FUNCTION  UTDE2 (A,B)
 C$    (Euclidean Norm of 2-Vector)
 C$    Return DSQRT(A**2+B**2) without  doing a  square root,  and
 C$    without destructive underflow or overflow.
 C$
 C$    This routine is  based on an  algorithm presented by  Cleve
 C$    Moler in 1979 and finally published and discussed in:
 C$
 C$    Cleve Moler and Donald Morrison, "Replacing Square Roots by
 C$    Pythagorean Sums",  IBM J.  Research and  Development,  27,
 C$    577-581 (1983).
 C$
 C$    Augustin A. Dubrulle, "A Class of Numerical Methods for the
 C$    Computation of  Pythagorean  Sums",  IBM  J.  Research  and
 C$    Development, 27, 582-589 (1983).
 C$
 C$    This version incorporates Dubrulle's  scaling for A,B  near
 C$    the  underflow  limit  to  preserve  accuracy.    Necessary
 C$    machine constants  are retrieved  at run-time  (only  once)
 C$    from the Port Library Framework.
 C$    (01-DEC-83)