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59 lines
1.9 KiB
59 lines
1.9 KiB
#include "clapack.h" |
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/* Subroutine */ int dlabad_(doublereal *small, doublereal *large) |
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{ |
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/* Builtin functions */ |
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double d_lg10(doublereal *), sqrt(doublereal); |
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/* -- LAPACK auxiliary routine (version 3.1) -- */ |
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/* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */ |
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/* November 2006 */ |
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/* .. Scalar Arguments .. */ |
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/* .. */ |
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/* Purpose */ |
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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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/* Arguments */ |
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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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/* 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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/* .. Intrinsic Functions .. */ |
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/* .. */ |
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/* .. Executable Statements .. */ |
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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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if (d_lg10(large) > 2e3) { |
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*small = sqrt(*small); |
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*large = sqrt(*large); |
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} |
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return 0; |
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/* End of DLABAD */ |
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} /* dlabad_ */
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