forked from lijiext/lammps
57 lines
1.8 KiB
Fortran
57 lines
1.8 KiB
Fortran
SUBROUTINE DLABAD( SMALL, LARGE )
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*
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* -- LAPACK auxiliary routine (version 3.2) --
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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 2006
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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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* Purpose
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* =======
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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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*
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* Arguments
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* =========
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*
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* SMALL (input/output) 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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*
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* LARGE (input/output) 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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*
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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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