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Annotation of rpl/lapack/lapack/dlapy2.f, revision 1.19

1.11      bertrand    1: *> \brief \b DLAPY2 returns sqrt(x2+y2).
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 DLAPY2 + dependencies
                     10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlapy2.f">
                     11: *> [TGZ]</a>
                     12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlapy2.f">
                     13: *> [ZIP]</a>
                     14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlapy2.f">
1.8       bertrand   15: *> [TXT]</a>
1.15      bertrand   16: *> \endhtmlonly
1.8       bertrand   17: *
                     18: *  Definition:
                     19: *  ===========
                     20: *
                     21: *       DOUBLE PRECISION FUNCTION DLAPY2( X, Y )
1.15      bertrand   22: *
1.8       bertrand   23: *       .. Scalar Arguments ..
                     24: *       DOUBLE PRECISION   X, Y
                     25: *       ..
1.15      bertrand   26: *
1.8       bertrand   27: *
                     28: *> \par Purpose:
                     29: *  =============
                     30: *>
                     31: *> \verbatim
                     32: *>
                     33: *> DLAPY2 returns sqrt(x**2+y**2), taking care not to cause unnecessary
1.19    ! bertrand   34: *> 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: *>          X and Y specify the values x and y.
                     49: *> \endverbatim
                     50: *
                     51: *  Authors:
                     52: *  ========
                     53: *
1.15      bertrand   54: *> \author Univ. of Tennessee
                     55: *> \author Univ. of California Berkeley
                     56: *> \author Univ. of Colorado Denver
                     57: *> \author NAG Ltd.
1.8       bertrand   58: *
1.15      bertrand   59: *> \ingroup OTHERauxiliary
1.8       bertrand   60: *
                     61: *  =====================================================================
1.1       bertrand   62:       DOUBLE PRECISION FUNCTION DLAPY2( X, Y )
                     63: *
1.19    ! bertrand   64: *  -- LAPACK auxiliary routine --
1.1       bertrand   65: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                     66: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
                     67: *
                     68: *     .. Scalar Arguments ..
                     69:       DOUBLE PRECISION   X, Y
                     70: *     ..
                     71: *
                     72: *  =====================================================================
                     73: *
                     74: *     .. Parameters ..
                     75:       DOUBLE PRECISION   ZERO
                     76:       PARAMETER          ( ZERO = 0.0D0 )
                     77:       DOUBLE PRECISION   ONE
                     78:       PARAMETER          ( ONE = 1.0D0 )
                     79: *     ..
                     80: *     .. Local Scalars ..
1.19    ! bertrand   81:       DOUBLE PRECISION   W, XABS, YABS, Z, HUGEVAL
1.17      bertrand   82:       LOGICAL            X_IS_NAN, Y_IS_NAN
                     83: *     ..
                     84: *     .. External Functions ..
                     85:       LOGICAL            DISNAN
                     86:       EXTERNAL           DISNAN
1.1       bertrand   87: *     ..
1.19    ! bertrand   88: *     .. External Subroutines ..
        !            89:       DOUBLE PRECISION   DLAMCH
        !            90: *     ..
1.1       bertrand   91: *     .. Intrinsic Functions ..
                     92:       INTRINSIC          ABS, MAX, MIN, SQRT
                     93: *     ..
                     94: *     .. Executable Statements ..
                     95: *
1.17      bertrand   96:       X_IS_NAN = DISNAN( X )
                     97:       Y_IS_NAN = DISNAN( Y )
                     98:       IF ( X_IS_NAN ) DLAPY2 = X
                     99:       IF ( Y_IS_NAN ) DLAPY2 = Y
1.19    ! bertrand  100:       HUGEVAL = DLAMCH( 'Overflow' )
1.17      bertrand  101: *
                    102:       IF ( .NOT.( X_IS_NAN.OR.Y_IS_NAN ) ) THEN
                    103:          XABS = ABS( X )
                    104:          YABS = ABS( Y )
                    105:          W = MAX( XABS, YABS )
                    106:          Z = MIN( XABS, YABS )
1.19    ! bertrand  107:          IF( Z.EQ.ZERO .OR. W.GT.HUGEVAL ) THEN
1.17      bertrand  108:             DLAPY2 = W
                    109:          ELSE
                    110:             DLAPY2 = W*SQRT( ONE+( Z / W )**2 )
                    111:          END IF
1.1       bertrand  112:       END IF
                    113:       RETURN
                    114: *
                    115: *     End of DLAPY2
                    116: *
                    117:       END