Return to dlabad.f CVS log

Up to [local] / rpl / lapack / lapack

Annotation of rpl/lapack/lapack/dlabad.f, revision 1.8

1.8     ! bertrand    1: *> \brief \b DLABAD
        !             2: *
        !             3: *  =========== DOCUMENTATION ===========
        !             4: *
        !             5: * Online html documentation available at 
        !             6: *            http://www.netlib.org/lapack/explore-html/ 
        !             7: *
        !             8: *> \htmlonly
        !             9: *> Download DLABAD + dependencies 
        !            10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlabad.f"> 
        !            11: *> [TGZ]</a> 
        !            12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlabad.f"> 
        !            13: *> [ZIP]</a> 
        !            14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlabad.f"> 
        !            15: *> [TXT]</a>
        !            16: *> \endhtmlonly 
        !            17: *
        !            18: *  Definition:
        !            19: *  ===========
        !            20: *
        !            21: *       SUBROUTINE DLABAD( SMALL, LARGE )
        !            22: * 
        !            23: *       .. Scalar Arguments ..
        !            24: *       DOUBLE PRECISION   LARGE, SMALL
        !            25: *       ..
        !            26: *  
        !            27: *
        !            28: *> \par Purpose:
        !            29: *  =============
        !            30: *>
        !            31: *> \verbatim
        !            32: *>
        !            33: *> DLABAD takes as input the values computed by DLAMCH for underflow and
        !            34: *> overflow, and returns the square root of each of these values if the
        !            35: *> log of LARGE is sufficiently large.  This subroutine is intended to
        !            36: *> identify machines with a large exponent range, such as the Crays, and
        !            37: *> redefine the underflow and overflow limits to be the square roots of
        !            38: *> the values computed by DLAMCH.  This subroutine is needed because
        !            39: *> DLAMCH does not compensate for poor arithmetic in the upper half of
        !            40: *> the exponent range, as is found on a Cray.
        !            41: *> \endverbatim
        !            42: *
        !            43: *  Arguments:
        !            44: *  ==========
        !            45: *
        !            46: *> \param[in,out] SMALL
        !            47: *> \verbatim
        !            48: *>          SMALL is DOUBLE PRECISION
        !            49: *>          On entry, the underflow threshold as computed by DLAMCH.
        !            50: *>          On exit, if LOG10(LARGE) is sufficiently large, the square
        !            51: *>          root of SMALL, otherwise unchanged.
        !            52: *> \endverbatim
        !            53: *>
        !            54: *> \param[in,out] LARGE
        !            55: *> \verbatim
        !            56: *>          LARGE is DOUBLE PRECISION
        !            57: *>          On entry, the overflow threshold as computed by DLAMCH.
        !            58: *>          On exit, if LOG10(LARGE) is sufficiently large, the square
        !            59: *>          root of LARGE, otherwise unchanged.
        !            60: *> \endverbatim
        !            61: *
        !            62: *  Authors:
        !            63: *  ========
        !            64: *
        !            65: *> \author Univ. of Tennessee 
        !            66: *> \author Univ. of California Berkeley 
        !            67: *> \author Univ. of Colorado Denver 
        !            68: *> \author NAG Ltd. 
        !            69: *
        !            70: *> \date November 2011
        !            71: *
        !            72: *> \ingroup auxOTHERauxiliary
        !            73: *
        !            74: *  =====================================================================
1.1       bertrand   75:       SUBROUTINE DLABAD( SMALL, LARGE )
                     76: *
1.8     ! bertrand   77: *  -- LAPACK auxiliary routine (version 3.4.0) --
1.1       bertrand   78: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                     79: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.8     ! bertrand   80: *     November 2011
1.1       bertrand   81: *
                     82: *     .. Scalar Arguments ..
                     83:       DOUBLE PRECISION   LARGE, SMALL
                     84: *     ..
                     85: *
                     86: *  =====================================================================
                     87: *
                     88: *     .. Intrinsic Functions ..
                     89:       INTRINSIC          LOG10, SQRT
                     90: *     ..
                     91: *     .. Executable Statements ..
                     92: *
                     93: *     If it looks like we're on a Cray, take the square root of
                     94: *     SMALL and LARGE to avoid overflow and underflow problems.
                     95: *
                     96:       IF( LOG10( LARGE ).GT.2000.D0 ) THEN
                     97:          SMALL = SQRT( SMALL )
                     98:          LARGE = SQRT( LARGE )
                     99:       END IF
                    100: *
                    101:       RETURN
                    102: *
                    103: *     End of DLABAD
                    104: *
                    105:       END