LAPACK  3.10.0
LAPACK: Linear Algebra PACKage
daxpy.f
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1 *> \brief \b DAXPY
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 * Definition:
9 * ===========
10 *
11 * SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
12 *
13 * .. Scalar Arguments ..
14 * DOUBLE PRECISION DA
15 * INTEGER INCX,INCY,N
16 * ..
17 * .. Array Arguments ..
18 * DOUBLE PRECISION DX(*),DY(*)
19 * ..
20 *
21 *
22 *> \par Purpose:
23 * =============
24 *>
25 *> \verbatim
26 *>
27 *> DAXPY constant times a vector plus a vector.
28 *> uses unrolled loops for increments equal to one.
29 *> \endverbatim
30 *
31 * Arguments:
32 * ==========
33 *
34 *> \param[in] N
35 *> \verbatim
36 *> N is INTEGER
37 *> number of elements in input vector(s)
38 *> \endverbatim
39 *>
40 *> \param[in] DA
41 *> \verbatim
42 *> DA is DOUBLE PRECISION
43 *> On entry, DA specifies the scalar alpha.
44 *> \endverbatim
45 *>
46 *> \param[in] DX
47 *> \verbatim
48 *> DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCX ) )
49 *> \endverbatim
50 *>
51 *> \param[in] INCX
52 *> \verbatim
53 *> INCX is INTEGER
54 *> storage spacing between elements of DX
55 *> \endverbatim
56 *>
57 *> \param[in,out] DY
58 *> \verbatim
59 *> DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1 )*abs( INCY ) )
60 *> \endverbatim
61 *>
62 *> \param[in] INCY
63 *> \verbatim
64 *> INCY is INTEGER
65 *> storage spacing between elements of DY
66 *> \endverbatim
67 *
68 * Authors:
69 * ========
70 *
71 *> \author Univ. of Tennessee
72 *> \author Univ. of California Berkeley
73 *> \author Univ. of Colorado Denver
74 *> \author NAG Ltd.
75 *
76 *> \ingroup double_blas_level1
77 *
78 *> \par Further Details:
79 * =====================
80 *>
81 *> \verbatim
82 *>
83 *> jack dongarra, linpack, 3/11/78.
84 *> modified 12/3/93, array(1) declarations changed to array(*)
85 *> \endverbatim
86 *>
87 * =====================================================================
88  SUBROUTINE daxpy(N,DA,DX,INCX,DY,INCY)
89 *
90 * -- Reference BLAS level1 routine --
91 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
92 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
93 *
94 * .. Scalar Arguments ..
95  DOUBLE PRECISION DA
96  INTEGER INCX,INCY,N
97 * ..
98 * .. Array Arguments ..
99  DOUBLE PRECISION DX(*),DY(*)
100 * ..
101 *
102 * =====================================================================
103 *
104 * .. Local Scalars ..
105  INTEGER I,IX,IY,M,MP1
106 * ..
107 * .. Intrinsic Functions ..
108  INTRINSIC mod
109 * ..
110  IF (n.LE.0) RETURN
111  IF (da.EQ.0.0d0) RETURN
112  IF (incx.EQ.1 .AND. incy.EQ.1) THEN
113 *
114 * code for both increments equal to 1
115 *
116 *
117 * clean-up loop
118 *
119  m = mod(n,4)
120  IF (m.NE.0) THEN
121  DO i = 1,m
122  dy(i) = dy(i) + da*dx(i)
123  END DO
124  END IF
125  IF (n.LT.4) RETURN
126  mp1 = m + 1
127  DO i = mp1,n,4
128  dy(i) = dy(i) + da*dx(i)
129  dy(i+1) = dy(i+1) + da*dx(i+1)
130  dy(i+2) = dy(i+2) + da*dx(i+2)
131  dy(i+3) = dy(i+3) + da*dx(i+3)
132  END DO
133  ELSE
134 *
135 * code for unequal increments or equal increments
136 * not equal to 1
137 *
138  ix = 1
139  iy = 1
140  IF (incx.LT.0) ix = (-n+1)*incx + 1
141  IF (incy.LT.0) iy = (-n+1)*incy + 1
142  DO i = 1,n
143  dy(iy) = dy(iy) + da*dx(ix)
144  ix = ix + incx
145  iy = iy + incy
146  END DO
147  END IF
148  RETURN
149 *
150 * End of DAXPY
151 *
152  END
subroutine daxpy(N, DA, DX, INCX, DY, INCY)
DAXPY
Definition: daxpy.f:89