ground/gcs/src/libs/eigen/lapack/dlapy3.f

   1 *> \brief \b DLAPY3
   2 *
   3 *  =========== DOCUMENTATION ===========
   4 *
   5 * Online html documentation available at
   6 *            http://www.netlib.org/lapack/explore-html/
   7 *
   8 *> \htmlonly
   9 *> Download DLAPY3 + dependencies
  10 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlapy3.f">
  11 *> [TGZ]</a>
  12 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlapy3.f">
  13 *> [ZIP]</a>
  14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlapy3.f">
  15 *> [TXT]</a>
  16 *> \endhtmlonly
  17 *
  18 *  Definition:
  19 *  ===========
  20 *
  21 *       DOUBLE PRECISION FUNCTION DLAPY3( X, Y, Z )
  22 *
  23 *       .. Scalar Arguments ..
  24 *       DOUBLE PRECISION   X, Y, Z
  25 *       ..
  26 *
  27 *
  28 *> \par Purpose:
  29 *  =============
  30 *>
  31 *> \verbatim
  32 *>
  33 *> DLAPY3 returns sqrt(x**2+y**2+z**2), taking care not to cause
  34 *> unnecessary overflow.
  35 *> \endverbatim
  36 *
  37 *  Arguments:
  38 *  ==========
  39 *
  40 *> \param[in] X
  41 *> \verbatim
  42 *>          X is DOUBLE PRECISION
  43 *> \endverbatim
  44 *>
  45 *> \param[in] Y
  46 *> \verbatim
  47 *>          Y is DOUBLE PRECISION
  48 *> \endverbatim
  49 *>
  50 *> \param[in] Z
  51 *> \verbatim
  52 *>          Z is DOUBLE PRECISION
  53 *>          X, Y and Z specify the values x, y and z.
  54 *> \endverbatim
  55 *
  56 *  Authors:
  57 *  ========
  58 *
  59 *> \author Univ. of Tennessee
  60 *> \author Univ. of California Berkeley
  61 *> \author Univ. of Colorado Denver
  62 *> \author NAG Ltd.
  63 *
  64 *> \date November 2011
  65 *
  66 *> \ingroup auxOTHERauxiliary
  67 *
  68 *  =====================================================================
  69       DOUBLE PRECISION FUNCTION DLAPY3( X, Y, Z )
  70 *
  71 *  -- LAPACK auxiliary routine (version 3.4.0) --
  72 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  73 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  74 *     November 2011
  75 *
  76 *     .. Scalar Arguments ..
  77       DOUBLE PRECISION   X, Y, Z
  78 *     ..
  79 *
  80 *  =====================================================================
  81 *
  82 *     .. Parameters ..
  83       DOUBLE PRECISION   ZERO
  84       PARAMETER          ( ZERO = 0.0D0 )
  85 *     ..
  86 *     .. Local Scalars ..
  87       DOUBLE PRECISION   W, XABS, YABS, ZABS
  88 *     ..
  89 *     .. Intrinsic Functions ..
  90       INTRINSIC          ABS, MAX, SQRT
  91 *     ..
  92 *     .. Executable Statements ..
  93 *
  94       XABS = ABS( X )
  95       YABS = ABS( Y )
  96       ZABS = ABS( Z )
  97       W = MAX( XABS, YABS, ZABS )
  98       IF( W.EQ.ZERO ) THEN
  99 *     W can be zero for max(0,nan,0)
 100 *     adding all three entries together will make sure
 101 *     NaN will not disappear.
 102          DLAPY3 =  XABS + YABS + ZABS
 103       ELSE
 104          DLAPY3 = W*SQRT( ( XABS / W )**2+( YABS / W )**2+
 105      $            ( ZABS / W )**2 )
 106       END IF
 107       RETURN
 108 *
 109 *     End of DLAPY3
 110 *
 111       END