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dscal

  1. C DSCAL     SOURCE    BP208322  22/09/16    21:15:06     11454          
  2. *> \brief \b DSCAL
  3. *
  4. *  =========== DOCUMENTATION ===========
  5. *
  6. * Online html documentation available at
  7. *            http://www.netlib.org/lapack/explore-html/
  8. *
  9. *  Definition:
  10. *  ===========
  11. *
  12. *       SUBROUTINE DSCAL(N,DA,DX,INCX)
  13. *
  14. *       .. Scalar Arguments ..
  15. *       REAL*8 DA
  16. *       INTEGER INCX,N
  17. *       ..
  18. *       .. Array Arguments ..
  19. *       REAL*8 DX(*)
  20. *       ..
  21. *
  22. *
  23. *> \par Purpose:
  24. *  =============
  25. *>
  26. *> \verbatim
  27. *>
  28. *>    DSCAL scales a vector by a constant.
  29. *>    uses unrolled loops for increment equal to 1.
  30. *> \endverbatim
  31. *
  32. *  Arguments:
  33. *  ==========
  34. *
  35. *> \param[in] N
  36. *> \verbatim
  37. *>          N is INTEGER
  38. *>         number of elements in input vector(s)
  39. *> \endverbatim
  40. *>
  41. *> \param[in] DA
  42. *> \verbatim
  43. *>          DA is REAL*8
  44. *>           On entry, DA specifies the scalar alpha.
  45. *> \endverbatim
  46. *>
  47. *> \param[in,out] DX
  48. *> \verbatim
  49. *>          DX is REAL*8 array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
  50. *> \endverbatim
  51. *>
  52. *> \param[in] INCX
  53. *> \verbatim
  54. *>          INCX is INTEGER
  55. *>         storage spacing between elements of DX
  56. *> \endverbatim
  57. *
  58. *  Authors:
  59. *  ========
  60. *
  61. *> \author Univ. of Tennessee
  62. *> \author Univ. of California Berkeley
  63. *> \author Univ. of Colorado Denver
  64. *> \author NAG Ltd.
  65. *
  66. *> \ingroup double_blas_level1
  67. *
  68. *> \par Further Details:
  69. *  =====================
  70. *>
  71. *> \verbatim
  72. *>
  73. *>     jack dongarra, linpack, 3/11/78.
  74. *>     modified 3/93 to return if incx .le. 0.
  75. *>     modified 12/3/93, array(1) declarations changed to array(*)
  76. *> \endverbatim
  77. *>
  78. *  =====================================================================
  79.       SUBROUTINE DSCAL(N,DA,DX,INCX)
  80. *
  81. *  -- Reference BLAS level1 routine --
  82. *  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
  83. *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  84. *
  85. *     .. Scalar Arguments ..
  86.       REAL*8 DA
  87.       INTEGER INCX,N
  88. *     ..
  89. *     .. Array Arguments ..
  90.       REAL*8 DX(*)
  91. *     ..
  92. *
  93. *  =====================================================================
  94. *
  95. *     .. Local Scalars ..
  96.       INTEGER I,M,MP1,NINCX
  97. *     ..
  98. *     .. Intrinsic Functions ..
  99. *     INTRINSIC MOD
  100. *     ..
  101.       IF (N.LE.0 .OR. INCX.LE.0) RETURN
  102.       IF (INCX.EQ.1) THEN
  103. *
  104. *        code for increment equal to 1
  105. *
  106. *
  107. *        clean-up loop
  108. *
  109.          M = MOD(N,5)
  110.          IF (M.NE.0) THEN
  111.             DO I = 1,M
  112.                DX(I) = DA*DX(I)
  113.             END DO
  114.             IF (N.LT.5) RETURN
  115.          END IF
  116.          MP1 = M + 1
  117.          DO I = MP1,N,5
  118.             DX(I) = DA*DX(I)
  119.             DX(I+1) = DA*DX(I+1)
  120.             DX(I+2) = DA*DX(I+2)
  121.             DX(I+3) = DA*DX(I+3)
  122.             DX(I+4) = DA*DX(I+4)
  123.          END DO
  124.       ELSE
  125. *
  126. *        code for increment not equal to 1
  127. *
  128.          NINCX = N*INCX
  129.          DO I = 1,NINCX,INCX
  130.             DX(I) = DA*DX(I)
  131.          END DO
  132.       END IF
  133.       RETURN
  134. *
  135. *     End of DSCAL
  136. *
  137.       END
  138.  
  139.  

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