[22] | 1 | *> \brief \b SLABAD |
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| 2 | * |
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| 3 | * =========== DOCUMENTATION =========== |
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| 4 | * |
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| 5 | * Online html documentation available at |
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| 6 | * http://www.netlib.org/lapack/explore-html/ |
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| 7 | * |
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| 8 | *> \htmlonly |
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| 9 | *> Download SLABAD + dependencies |
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| 10 | *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slabad.f"> |
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| 11 | *> [TGZ]</a> |
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| 12 | *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slabad.f"> |
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| 13 | *> [ZIP]</a> |
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| 14 | *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slabad.f"> |
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| 15 | *> [TXT]</a> |
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| 16 | *> \endhtmlonly |
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| 17 | * |
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| 18 | * Definition: |
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| 19 | * =========== |
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| 20 | * |
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| 21 | * SUBROUTINE SLABAD( SMALL, LARGE ) |
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| 22 | * |
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| 23 | * .. Scalar Arguments .. |
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| 24 | * REAL LARGE, SMALL |
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| 25 | * .. |
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| 26 | * |
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| 27 | * |
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| 28 | *> \par Purpose: |
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| 29 | * ============= |
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| 30 | *> |
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| 31 | *> \verbatim |
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| 32 | *> |
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| 33 | *> SLABAD takes as input the values computed by SLAMCH for underflow and |
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| 34 | *> overflow, and returns the square root of each of these values if the |
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| 35 | *> log of LARGE is sufficiently large. This subroutine is intended to |
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| 36 | *> identify machines with a large exponent range, such as the Crays, and |
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| 37 | *> redefine the underflow and overflow limits to be the square roots of |
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| 38 | *> the values computed by SLAMCH. This subroutine is needed because |
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| 39 | *> SLAMCH does not compensate for poor arithmetic in the upper half of |
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| 40 | *> the exponent range, as is found on a Cray. |
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| 41 | *> \endverbatim |
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| 42 | * |
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| 43 | * Arguments: |
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| 44 | * ========== |
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| 45 | * |
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| 46 | *> \param[in,out] SMALL |
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| 47 | *> \verbatim |
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| 48 | *> SMALL is REAL |
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| 49 | *> On entry, the underflow threshold as computed by SLAMCH. |
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| 50 | *> On exit, if LOG10(LARGE) is sufficiently large, the square |
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| 51 | *> root of SMALL, otherwise unchanged. |
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| 52 | *> \endverbatim |
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| 53 | *> |
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| 54 | *> \param[in,out] LARGE |
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| 55 | *> \verbatim |
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| 56 | *> LARGE is REAL |
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| 57 | *> On entry, the overflow threshold as computed by SLAMCH. |
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| 58 | *> On exit, if LOG10(LARGE) is sufficiently large, the square |
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| 59 | *> root of LARGE, otherwise unchanged. |
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| 60 | *> \endverbatim |
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| 61 | * |
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| 62 | * Authors: |
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| 63 | * ======== |
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| 64 | * |
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| 65 | *> \author Univ. of Tennessee |
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| 66 | *> \author Univ. of California Berkeley |
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| 67 | *> \author Univ. of Colorado Denver |
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| 68 | *> \author NAG Ltd. |
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| 69 | * |
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| 70 | *> \date November 2011 |
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| 71 | * |
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| 72 | *> \ingroup auxOTHERauxiliary |
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| 73 | * |
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| 74 | * ===================================================================== |
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| 75 | SUBROUTINE SLABAD( SMALL, LARGE ) |
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| 76 | * |
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| 77 | * -- LAPACK auxiliary routine (version 3.4.0) -- |
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| 78 | * -- LAPACK is a software package provided by Univ. of Tennessee, -- |
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| 79 | * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- |
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| 80 | * November 2011 |
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| 81 | * |
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| 82 | * .. Scalar Arguments .. |
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| 83 | REAL LARGE, SMALL |
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| 84 | * .. |
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| 85 | * |
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| 86 | * ===================================================================== |
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| 87 | * |
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| 88 | * .. Intrinsic Functions .. |
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| 89 | INTRINSIC LOG10, SQRT |
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| 90 | * .. |
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| 91 | * .. Executable Statements .. |
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| 92 | * |
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| 93 | * If it looks like we're on a Cray, take the square root of |
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| 94 | * SMALL and LARGE to avoid overflow and underflow problems. |
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| 95 | * |
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| 96 | IF( LOG10( LARGE ).GT.2000. ) THEN |
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| 97 | SMALL = SQRT( SMALL ) |
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| 98 | LARGE = SQRT( LARGE ) |
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| 99 | END IF |
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| 100 | * |
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| 101 | RETURN |
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| 102 | * |
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| 103 | * End of SLABAD |
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| 104 | * |
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| 105 | END |
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