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Annotation of rpl/lapack/lapack/dlabad.f, revision 1.16

1.8       bertrand    1: *> \brief \b DLABAD
                      2: *
                      3: *  =========== DOCUMENTATION ===========
                      4: *
1.14      bertrand    5: * Online html documentation available at
                      6: *            http://www.netlib.org/lapack/explore-html/
1.8       bertrand    7: *
                      8: *> \htmlonly
1.14      bertrand    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">
1.8       bertrand   15: *> [TXT]</a>
1.14      bertrand   16: *> \endhtmlonly
1.8       bertrand   17: *
                     18: *  Definition:
                     19: *  ===========
                     20: *
                     21: *       SUBROUTINE DLABAD( SMALL, LARGE )
1.14      bertrand   22: *
1.8       bertrand   23: *       .. Scalar Arguments ..
                     24: *       DOUBLE PRECISION   LARGE, SMALL
                     25: *       ..
1.14      bertrand   26: *
1.8       bertrand   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: *
1.14      bertrand   65: *> \author Univ. of Tennessee
                     66: *> \author Univ. of California Berkeley
                     67: *> \author Univ. of Colorado Denver
                     68: *> \author NAG Ltd.
1.8       bertrand   69: *
1.14      bertrand   70: *> \date December 2016
1.8       bertrand   71: *
1.14      bertrand   72: *> \ingroup OTHERauxiliary
1.8       bertrand   73: *
                     74: *  =====================================================================
1.1       bertrand   75:       SUBROUTINE DLABAD( SMALL, LARGE )
                     76: *
1.14      bertrand   77: *  -- LAPACK auxiliary routine (version 3.7.0) --
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..--
1.14      bertrand   80: *     December 2016
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