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