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dlapy2

  1. C DLAPY2    SOURCE    PV        22/04/19    16:18:02     11344          
  2. *> \brief \b DLAPY2 returns sqrt(x2+y2).
  3. *
  4. *  =========== DOCUMENTATION ===========
  5. *
  6. * Online html documentation available at
  7. *            http://www.netlib.org/lapack/explore-html/
  8. *
  9. *> \htmlonly
  10. *> Download DLAPY2 + dependencies
  11. *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlapy2.f">
  12. *> [TGZ]</a>
  13. *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlapy2.f">
  14. *> [ZIP]</a>
  15. *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlapy2.f">
  16. *> [TXT]</a>
  17. *> \endhtmlonly
  18. *
  19. *  Definition:
  20. *  ===========
  21. *
  22. *       REAL*8 FUNCTION DLAPY2( X, Y )
  23. *
  24. *       .. Scalar Arguments ..
  25. *       REAL*8   X, Y
  26. *       ..
  27. *
  28. *
  29. *> \par Purpose:
  30. *  =============
  31. *>
  32. *> \verbatim
  33. *>
  34. *> DLAPY2 returns sqrt(x**2+y**2), taking care not to cause unnecessary
  35. *> overflow.
  36. *> \endverbatim
  37. *
  38. *  Arguments:
  39. *  ==========
  40. *
  41. *> \param[in] X
  42. *> \verbatim
  43. *>          X is DOUBLE PRECISION
  44. *> \endverbatim
  45. *>
  46. *> \param[in] Y
  47. *> \verbatim
  48. *>          Y is DOUBLE PRECISION
  49. *>          X and Y specify the values x and y.
  50. *> \endverbatim
  51. *
  52. *  Authors:
  53. *  ========
  54. *
  55. *> \author Univ. of Tennessee
  56. *> \author Univ. of California Berkeley
  57. *> \author Univ. of Colorado Denver
  58. *> \author NAG Ltd.
  59. *
  60. *> \date June 2017
  61. *
  62. *> \ingroup OTHERauxiliary
  63. *
  64. *  =====================================================================
  65.       FUNCTION DLAPY2( X, Y )
  66. *
  67. *  -- LAPACK auxiliary routine (version 3.7.1) --
  68. *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  69. *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  70. *     June 2017
  71. *
  72. *     .. Scalar Arguments ..
  73.       REAL*8   DLAPY2
  74.       REAL*8   X, Y
  75. *     ..
  76. *
  77. *  =====================================================================
  78. *
  79. *     .. Parameters ..
  80.       REAL*8   ZERO
  81.       PARAMETER          ( ZERO = 0.0D0 )
  82.       REAL*8   ONE
  83.       PARAMETER          ( ONE = 1.0D0 )
  84. *     ..
  85. *     .. Local Scalars ..
  86.       REAL*8   W, XABS, YABS, Z
  87.       LOGICAL            X_IS_NAN, Y_IS_NAN
  88. *     ..
  89. *     .. External Functions ..
  90.       LOGICAL            DISNAN
  91.       EXTERNAL           DISNAN
  92. *     ..
  93. **     .. Intrinsic Functions ..
  94. *      INTRINSIC          ABS, MAX, MIN, SQRT
  95. **     ..
  96. **     .. Executable Statements ..
  97. *
  98.       DLAPY2 = 0.D0
  99.       X_IS_NAN = DISNAN( X )
  100.       Y_IS_NAN = DISNAN( Y )
  101.       IF ( X_IS_NAN ) DLAPY2 = X
  102.       IF ( Y_IS_NAN ) DLAPY2 = Y
  103. *
  104.       IF ( .NOT.( X_IS_NAN.OR.Y_IS_NAN ) ) THEN
  105.          XABS = ABS( X )
  106.          YABS = ABS( Y )
  107.          W = MAX( XABS, YABS )
  108.          Z = MIN( XABS, YABS )
  109.          IF( Z.EQ.ZERO ) THEN
  110.             DLAPY2 = W
  111.          ELSE
  112.             DLAPY2 = W*SQRT( ONE+( Z / W )**2 )
  113.          END IF
  114.       END IF
  115.       RETURN
  116. *
  117. *     End of DLAPY2
  118. *
  119.       END
  120.  
  121.  
  122.  
  123.  

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