slapy3.f

Go to the documentation of this file.

*> \brief \b SLAPY3 returns sqrt(x2+y2+z2).
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*> Download SLAPY3 + dependencies
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slapy3.f">
*> [TGZ]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slapy3.f">
*> [ZIP]</a>
*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slapy3.f">
*> [TXT]</a>
*
*  Definition:
*  ===========
*
*       REAL             FUNCTION SLAPY3( X, Y, Z )
*
*       .. Scalar Arguments ..
*       REAL               X, Y, Z
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*> SLAPY3 returns sqrt(x**2+y**2+z**2), taking care not to cause
*> unnecessary overflow and unnecessary underflow.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] X
*> \verbatim
*>          X is REAL
*> \endverbatim
*>
*> \param[in] Y
*> \verbatim
*>          Y is REAL
*> \endverbatim
*>
*> \param[in] Z
*> \verbatim
*>          Z is REAL
*>          X, Y and Z specify the values x, y and z.
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \ingroup lapy3
*
*  =====================================================================
      REAL             function slapy3( x, y, z )
*
*  -- LAPACK auxiliary routine --
*  -- LAPACK is a software package provided by Univ. of Tennessee,    --
*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
*
*     .. Scalar Arguments ..
      REAL               x, y, z
*     ..
*
*  =====================================================================
*
*     .. Parameters ..
      REAL               zero
      parameter( zero = 0.0e0 )
*     ..
*     .. Local Scalars ..
      REAL               w, xabs, yabs, zabs, hugeval
*     ..
*     .. External Subroutines ..
      REAL               slamch
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          abs, max, sqrt
*     ..
*     .. Executable Statements ..
*
      hugeval = slamch( 'Overflow' )
      xabs = abs( x )
      yabs = abs( y )
      zabs = abs( z )
      w = max( xabs, yabs, zabs )
      IF( w.EQ.zero .OR. w.GT.hugeval ) THEN
*     W can be zero for max(0,nan,0)
*     adding all three entries together will make sure
*     NaN will not disappear.
         slapy3 =  xabs + yabs + zabs
      ELSE
         slapy3 = w*sqrt( ( xabs / w )**2+( yabs / w )**2+
     $            ( zabs / w )**2 )
      END IF
      RETURN
*
*     End of SLAPY3
*
      END