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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