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Annotation of rpl/lapack/lapack/dlapy3.f, revision 1.18

1.11      bertrand    1: *> \brief \b DLAPY3 returns sqrt(x2+y2+z2).
1.8       bertrand    2: *
                      3: *  =========== DOCUMENTATION ===========
                      4: *
1.15      bertrand    5: * Online html documentation available at
                      6: *            http://www.netlib.org/lapack/explore-html/
1.8       bertrand    7: *
                      8: *> \htmlonly
1.15      bertrand    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">
1.8       bertrand   15: *> [TXT]</a>
1.15      bertrand   16: *> \endhtmlonly
1.8       bertrand   17: *
                     18: *  Definition:
                     19: *  ===========
                     20: *
                     21: *       DOUBLE PRECISION FUNCTION DLAPY3( X, Y, Z )
1.15      bertrand   22: *
1.8       bertrand   23: *       .. Scalar Arguments ..
                     24: *       DOUBLE PRECISION   X, Y, Z
                     25: *       ..
1.15      bertrand   26: *
1.8       bertrand   27: *
                     28: *> \par Purpose:
                     29: *  =============
                     30: *>
                     31: *> \verbatim
                     32: *>
                     33: *> DLAPY3 returns sqrt(x**2+y**2+z**2), taking care not to cause
1.18    ! bertrand   34: *> unnecessary overflow and unnecessary underflow.
1.8       bertrand   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: *
1.15      bertrand   59: *> \author Univ. of Tennessee
                     60: *> \author Univ. of California Berkeley
                     61: *> \author Univ. of Colorado Denver
                     62: *> \author NAG Ltd.
1.8       bertrand   63: *
1.15      bertrand   64: *> \ingroup OTHERauxiliary
1.8       bertrand   65: *
                     66: *  =====================================================================
1.1       bertrand   67:       DOUBLE PRECISION FUNCTION DLAPY3( X, Y, Z )
                     68: *
1.18    ! bertrand   69: *  -- LAPACK auxiliary routine --
1.1       bertrand   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 ..
1.18    ! bertrand   84:       DOUBLE PRECISION   W, XABS, YABS, ZABS, HUGEVAL
        !            85: *     ..
        !            86: *     .. External Subroutines ..
        !            87:       DOUBLE PRECISION   DLAMCH
1.1       bertrand   88: *     ..
                     89: *     .. Intrinsic Functions ..
                     90:       INTRINSIC          ABS, MAX, SQRT
                     91: *     ..
                     92: *     .. Executable Statements ..
                     93: *
1.18    ! bertrand   94:       HUGEVAL = DLAMCH( 'Overflow' )
1.1       bertrand   95:       XABS = ABS( X )
                     96:       YABS = ABS( Y )
                     97:       ZABS = ABS( Z )
                     98:       W = MAX( XABS, YABS, ZABS )
1.18    ! bertrand   99:       IF( W.EQ.ZERO .OR. W.GT.HUGEVAL ) THEN
1.1       bertrand  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