dlapy3.f

          DOUBLE PRECISION FUNCTION DLAPY3( X, Y, Z )
    *
    *  -- LAPACK auxiliary routine (version 3.1) --
    *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
    *     November 2006
    *
    *     .. Scalar Arguments ..
          DOUBLE PRECISION   X, Y, Z
    *     ..
    *
    *  Purpose
    *  =======
    *
    *  DLAPY3 returns sqrt(x**2+y**2+z**2), taking care not to cause
    *  unnecessary overflow.
    *
    *  Arguments
    *  =========
    *
    *  X       (input) DOUBLE PRECISION
    *  Y       (input) DOUBLE PRECISION
    *  Z       (input) DOUBLE PRECISION
    *          X, Y and Z specify the values x, y and z.
    *
    *  =====================================================================
    *
    *     .. Parameters ..
          DOUBLE PRECISION   ZERO
          PARAMETER          ( ZERO = 0.0D0 )
    *     ..
    *     .. Local Scalars ..
          DOUBLE PRECISION   W, XABS, YABS, ZABS
    *     ..
    *     .. Intrinsic Functions ..
          INTRINSIC          ABS, MAX, SQRT
    *     ..
    *     .. Executable Statements ..
    *
          XABS = ABS( X )
          YABS = ABS( Y )
          ZABS = ABS( Z )
          W = MAX( XABS, YABS, ZABS )
          IF( W.EQ.ZERO ) THEN
    *     W can be zero for max(0,nan,0)
    *     adding all three entries together will make sure
    *     NaN will not disappear.
             DLAPY3 =  XABS + YABS + ZABS
          ELSE
             DLAPY3 = W*SQRT( ( XABS / W )**2+( YABS / W )**2+
         $            ( ZABS / W )**2 )
          END IF
          RETURN
    *
    *     End of DLAPY3
    *
          END