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60 lines
1.9 KiB
C
60 lines
1.9 KiB
C
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#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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