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    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: *> \ingroup OTHERauxiliary
   71: *
   72: *  =====================================================================
   73:       SUBROUTINE DLABAD( SMALL, LARGE )
   74: *
   75: *  -- LAPACK auxiliary routine --
   76: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
   77: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   78: *
   79: *     .. Scalar Arguments ..
   80:       DOUBLE PRECISION   LARGE, SMALL
   81: *     ..
   82: *
   83: *  =====================================================================
   84: *
   85: *     .. Intrinsic Functions ..
   86:       INTRINSIC          LOG10, SQRT
   87: *     ..
   88: *     .. Executable Statements ..
   89: *
   90: *     If it looks like we're on a Cray, take the square root of
   91: *     SMALL and LARGE to avoid overflow and underflow problems.
   92: *
   93:       IF( LOG10( LARGE ).GT.2000.D0 ) THEN
   94:          SMALL = SQRT( SMALL )
   95:          LARGE = SQRT( LARGE )
   96:       END IF
   97: *
   98:       RETURN
   99: *
  100: *     End of DLABAD
  101: *
  102:       END