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UTRE3

       REAL FUNCTION  UTRE3 (VX,VY,VZ)
 C$    (Euclidean Norm of 3-Vector)
 C$    Return as  a  function  value the  Euclidean  norm  of  the
 C$    3-vector, (VX,VY,VZ).  This is  equivalent to SQRT(VX**2  +
 C$    VY**2  +  VZ**2),  but  this  expression  can  overflow  or
 C$    underflow over roughly half the range of REAL numbers.  The
 C$    algorithm used is stable over the entire range.
 C$    (09-APR-82)