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*  Authors:
32*  ========
33*
34*> \author Univ. of Tennessee
35*> \author Univ. of California Berkeley
36*> \author Univ. of Colorado Denver
37*> \author NAG Ltd.
38*
39*> \date November 2011
40*
41*> \ingroup double_blas_level1
42*
43*> \par Further Details:
44*  =====================
45*>
46*> \verbatim
47*>
48*>     jack dongarra, linpack, 3/11/78.
49*>     modified 12/3/93, array(1) declarations changed to array(*)
50*> \endverbatim
51*>
52*  =====================================================================
53      SUBROUTINE DAXPY(N,DA,DX,INCX,DY,INCY)
54*
55*  -- Reference BLAS level1 routine (version 3.4.0) --
56*  -- Reference BLAS is a software package provided by Univ. of Tennessee,    --
57*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
58*     November 2011
59*
60*     .. Scalar Arguments ..
61      DOUBLE PRECISION DA
62      INTEGER INCX,INCY,N
63*     ..
64*     .. Array Arguments ..
65      DOUBLE PRECISION DX(*),DY(*)
66*     ..
67*
68*  =====================================================================
69*
70*     .. Local Scalars ..
71      INTEGER I,IX,IY,M,MP1
72*     ..
73*     .. Intrinsic Functions ..
74      INTRINSIC MOD
75*     ..
76      IF (N.LE.0) RETURN
77      IF (DA.EQ.0.0d0) RETURN
78      IF (INCX.EQ.1 .AND. INCY.EQ.1) THEN
79*
80*        code for both increments equal to 1
81*
82*
83*        clean-up loop
84*
85         M = MOD(N,4)
86         IF (M.NE.0) THEN
87            DO I = 1,M
88               DY(I) = DY(I) + DA*DX(I)
89            END DO
90         END IF
91         IF (N.LT.4) RETURN
92         MP1 = M + 1
93         DO I = MP1,N,4
94            DY(I) = DY(I) + DA*DX(I)
95            DY(I+1) = DY(I+1) + DA*DX(I+1)
96            DY(I+2) = DY(I+2) + DA*DX(I+2)
97            DY(I+3) = DY(I+3) + DA*DX(I+3)
98         END DO
99      ELSE
100*
101*        code for unequal increments or equal increments
102*          not equal to 1
103*
104         IX = 1
105         IY = 1
106         IF (INCX.LT.0) IX = (-N+1)*INCX + 1
107         IF (INCY.LT.0) IY = (-N+1)*INCY + 1
108         DO I = 1,N
109          DY(IY) = DY(IY) + DA*DX(IX)
110          IX = IX + INCX
111          IY = IY + INCY
112         END DO
113      END IF
114      RETURN
115      END
116