106 lines
3.0 KiB
Fortran
106 lines
3.0 KiB
Fortran
*> \brief \b DLABAD
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*
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* =========== DOCUMENTATION ===========
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*
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* Online html documentation available at
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* http://www.netlib.org/lapack/explore-html/
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*
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*> \htmlonly
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*> Download DLABAD + dependencies
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlabad.f">
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*> [TGZ]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlabad.f">
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*> [ZIP]</a>
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*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlabad.f">
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*> [TXT]</a>
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*> \endhtmlonly
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*
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* Definition:
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* ===========
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*
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* SUBROUTINE DLABAD( SMALL, LARGE )
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*
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* .. Scalar Arguments ..
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* DOUBLE PRECISION LARGE, SMALL
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* ..
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*
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*
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*> \par Purpose:
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* =============
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*>
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*> \verbatim
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*>
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*> DLABAD takes as input the values computed by DLAMCH for underflow and
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*> overflow, and returns the square root of each of these values if the
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*> log of LARGE is sufficiently large. This subroutine is intended to
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*> identify machines with a large exponent range, such as the Crays, and
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*> redefine the underflow and overflow limits to be the square roots of
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*> the values computed by DLAMCH. This subroutine is needed because
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*> DLAMCH does not compensate for poor arithmetic in the upper half of
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*> the exponent range, as is found on a Cray.
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*> \endverbatim
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*
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* Arguments:
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* ==========
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*
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*> \param[in,out] SMALL
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*> \verbatim
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*> SMALL is DOUBLE PRECISION
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*> On entry, the underflow threshold as computed by DLAMCH.
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*> On exit, if LOG10(LARGE) is sufficiently large, the square
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*> root of SMALL, otherwise unchanged.
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*> \endverbatim
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*>
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*> \param[in,out] LARGE
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*> \verbatim
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*> LARGE is DOUBLE PRECISION
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*> On entry, the overflow threshold as computed by DLAMCH.
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*> On exit, if LOG10(LARGE) is sufficiently large, the square
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*> root of LARGE, otherwise unchanged.
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*> \endverbatim
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*
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* Authors:
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* ========
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*
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*> \author Univ. of Tennessee
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*> \author Univ. of California Berkeley
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*> \author Univ. of Colorado Denver
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*> \author NAG Ltd.
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*
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*> \date November 2011
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*
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*> \ingroup auxOTHERauxiliary
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*
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* =====================================================================
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SUBROUTINE DLABAD( SMALL, LARGE )
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*
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* -- LAPACK auxiliary routine (version 3.4.0) --
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* -- LAPACK is a software package provided by Univ. of Tennessee, --
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* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
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* November 2011
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*
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* .. Scalar Arguments ..
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DOUBLE PRECISION LARGE, SMALL
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* ..
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*
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* =====================================================================
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*
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* .. Intrinsic Functions ..
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INTRINSIC LOG10, SQRT
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* ..
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* .. Executable Statements ..
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*
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* If it looks like we're on a Cray, take the square root of
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* SMALL and LARGE to avoid overflow and underflow problems.
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*
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IF( LOG10( LARGE ).GT.2000.D0 ) THEN
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SMALL = SQRT( SMALL )
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LARGE = SQRT( LARGE )
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END IF
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*
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RETURN
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*
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* End of DLABAD
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*
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END
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