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dlabad

  1. C DLABAD    SOURCE    BP208322  18/07/10    21:15:04     9872           
  2. *> \brief \b DLABAD
  3. *
  4. *  =========== DOCUMENTATION ===========
  5. *
  6. * Online html documentation available at
  7. *            http://www.netlib.org/lapack/explore-html/
  8. *
  9. *> \htmlonly
  10. *> Download DLABAD + dependencies
  11. *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlabad.f">
  12. *> [TGZ]</a>
  13. *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlabad.f">
  14. *> [ZIP]</a>
  15. *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlabad.f">
  16. *> [TXT]</a>
  17. *> \endhtmlonly
  18. *
  19. *  Definition:
  20. *  ===========
  21. *
  22. *       SUBROUTINE DLABAD( SMALL, LARGE )
  23. *
  24. *       .. Scalar Arguments ..
  25. *       REAL*8   LARGE, SMALL
  26. *       ..
  27. *
  28. *
  29. *> \par Purpose:
  30. *  =============
  31. *>
  32. *> \verbatim
  33. *>
  34. *> DLABAD takes as input the values computed by DLAMCH for underflow and
  35. *> overflow, and returns the square root of each of these values if the
  36. *> log of LARGE is sufficiently large.  This subroutine is intended to
  37. *> identify machines with a large exponent range, such as the Crays, and
  38. *> redefine the underflow and overflow limits to be the square roots of
  39. *> the values computed by DLAMCH.  This subroutine is needed because
  40. *> DLAMCH does not compensate for poor arithmetic in the upper half of
  41. *> the exponent range, as is found on a Cray.
  42. *> \endverbatim
  43. *
  44. *  Arguments:
  45. *  ==========
  46. *
  47. *> \param[in,out] SMALL
  48. *> \verbatim
  49. *>          SMALL is DOUBLE PRECISION
  50. *>          On entry, the underflow threshold as computed by DLAMCH.
  51. *>          On exit, if LOG10(LARGE) is sufficiently large, the square
  52. *>          root of SMALL, otherwise unchanged.
  53. *> \endverbatim
  54. *>
  55. *> \param[in,out] LARGE
  56. *> \verbatim
  57. *>          LARGE is DOUBLE PRECISION
  58. *>          On entry, the overflow threshold as computed by DLAMCH.
  59. *>          On exit, if LOG10(LARGE) is sufficiently large, the square
  60. *>          root of LARGE, otherwise unchanged.
  61. *> \endverbatim
  62. *
  63. *  Authors:
  64. *  ========
  65. *
  66. *> \author Univ. of Tennessee
  67. *> \author Univ. of California Berkeley
  68. *> \author Univ. of Colorado Denver
  69. *> \author NAG Ltd.
  70. *
  71. *> \date December 2016
  72. *
  73. *> \ingroup OTHERauxiliary
  74. *
  75. *  =====================================================================
  76.       SUBROUTINE DLABAD( SMALL, LARGE )
  77. *
  78. *  -- LAPACK auxiliary routine (version 3.7.0) --
  79. *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  80. *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  81. *     December 2016
  82. *
  83. *     .. Scalar Arguments ..
  84.       REAL*8   LARGE, SMALL
  85. *     ..
  86. *
  87. *  =====================================================================
  88. *
  89. **     .. Intrinsic Functions ..
  90. *      INTRINSIC          LOG10, SQRT
  91. **     ..
  92. **     .. Executable Statements ..
  93. *
  94. *     If it looks like we're on a Cray, take the square root of
  95. *     SMALL and LARGE to avoid overflow and underflow problems.
  96. *
  97.       IF( LOG10( LARGE ).GT.2000.D0 ) THEN
  98.          SMALL = SQRT( SMALL )
  99.          LARGE = SQRT( LARGE )
  100.       END IF
  101. *
  102.       RETURN
  103. *
  104. *     End of DLABAD
  105. *
  106.       END
  107.  
  108.  
  109.  

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