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    1: *> \brief \b DLAPY3 returns sqrt(x2+y2+z2).
    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 and unnecessary underflow.
   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: *> \ingroup OTHERauxiliary
   65: *
   66: *  =====================================================================
   67:       DOUBLE PRECISION FUNCTION DLAPY3( X, Y, Z )
   68: *
   69: *  -- LAPACK auxiliary routine --
   70: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
   71: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   72: *
   73: *     .. Scalar Arguments ..
   74:       DOUBLE PRECISION   X, Y, Z
   75: *     ..
   76: *
   77: *  =====================================================================
   78: *
   79: *     .. Parameters ..
   80:       DOUBLE PRECISION   ZERO
   81:       PARAMETER          ( ZERO = 0.0D0 )
   82: *     ..
   83: *     .. Local Scalars ..
   84:       DOUBLE PRECISION   W, XABS, YABS, ZABS, HUGEVAL
   85: *     ..
   86: *     .. External Subroutines ..
   87:       DOUBLE PRECISION   DLAMCH
   88: *     ..
   89: *     .. Intrinsic Functions ..
   90:       INTRINSIC          ABS, MAX, SQRT
   91: *     ..
   92: *     .. Executable Statements ..
   93: *
   94:       HUGEVAL = DLAMCH( 'Overflow' )
   95:       XABS = ABS( X )
   96:       YABS = ABS( Y )
   97:       ZABS = ABS( Z )
   98:       W = MAX( XABS, YABS, ZABS )
   99:       IF( W.EQ.ZERO .OR. W.GT.HUGEVAL ) THEN
  100: *     W can be zero for max(0,nan,0)
  101: *     adding all three entries together will make sure
  102: *     NaN will not disappear.
  103:          DLAPY3 =  XABS + YABS + ZABS
  104:       ELSE
  105:          DLAPY3 = W*SQRT( ( XABS / W )**2+( YABS / W )**2+
  106:      $            ( ZABS / W )**2 )
  107:       END IF
  108:       RETURN
  109: *
  110: *     End of DLAPY3
  111: *
  112:       END