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来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 78 行
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SUBROUTINE <a name="SLABAD.1"></a><a href="slabad.f.html#SLABAD.1">SLABAD</a>( SMALL, LARGE )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> -- LAPACK auxiliary routine (version 3.1) --
</span><span class="comment">*</span><span class="comment"> Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment"> November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> .. Scalar Arguments ..
</span> REAL LARGE, SMALL
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> Purpose
</span><span class="comment">*</span><span class="comment"> =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> <a name="SLABAD.14"></a><a href="slabad.f.html#SLABAD.1">SLABAD</a> takes as input the values computed by <a name="SLAMCH.14"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a> for underflow and
</span><span class="comment">*</span><span class="comment"> overflow, and returns the square root of each of these values if the
</span><span class="comment">*</span><span class="comment"> log of LARGE is sufficiently large. This subroutine is intended to
</span><span class="comment">*</span><span class="comment"> identify machines with a large exponent range, such as the Crays, and
</span><span class="comment">*</span><span class="comment"> redefine the underflow and overflow limits to be the square roots of
</span><span class="comment">*</span><span class="comment"> the values computed by <a name="SLAMCH.19"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>. This subroutine is needed because
</span><span class="comment">*</span><span class="comment"> <a name="SLAMCH.20"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a> does not compensate for poor arithmetic in the upper half of
</span><span class="comment">*</span><span class="comment"> the exponent range, as is found on a Cray.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> Arguments
</span><span class="comment">*</span><span class="comment"> =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> SMALL (input/output) REAL
</span><span class="comment">*</span><span class="comment"> On entry, the underflow threshold as computed by <a name="SLAMCH.27"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>.
</span><span class="comment">*</span><span class="comment"> On exit, if LOG10(LARGE) is sufficiently large, the square
</span><span class="comment">*</span><span class="comment"> root of SMALL, otherwise unchanged.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> LARGE (input/output) REAL
</span><span class="comment">*</span><span class="comment"> On entry, the overflow threshold as computed by <a name="SLAMCH.32"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>.
</span><span class="comment">*</span><span class="comment"> On exit, if LOG10(LARGE) is sufficiently large, the square
</span><span class="comment">*</span><span class="comment"> root of LARGE, otherwise unchanged.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> .. Intrinsic Functions ..
</span> INTRINSIC LOG10, SQRT
<span class="comment">*</span><span class="comment"> ..
</span><span class="comment">*</span><span class="comment"> .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> If it looks like we're on a Cray, take the square root of
</span><span class="comment">*</span><span class="comment"> SMALL and LARGE to avoid overflow and underflow problems.
</span><span class="comment">*</span><span class="comment">
</span> IF( LOG10( LARGE ).GT.2000. ) THEN
SMALL = SQRT( SMALL )
LARGE = SQRT( LARGE )
END IF
<span class="comment">*</span><span class="comment">
</span> RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> End of <a name="SLABAD.53"></a><a href="slabad.f.html#SLABAD.1">SLABAD</a>
</span><span class="comment">*</span><span class="comment">
</span> END
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